U.S. patent application number 12/185499 was filed with the patent office on 2009-02-12 for organic electroluminescent device and electronic apparatus.
This patent application is currently assigned to Seiko Epson Corporation. Invention is credited to Toshihiro ODA.
Application Number | 20090039777 12/185499 |
Document ID | / |
Family ID | 40345817 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090039777 |
Kind Code |
A1 |
ODA; Toshihiro |
February 12, 2009 |
ORGANIC ELECTROLUMINESCENT DEVICE AND ELECTRONIC APPARATUS
Abstract
An organic electroluminescent device includes a translucent
first electrode, a translucent second electrode, a luminescent
layer, a reflective layer, and a transflective layer. The
luminescent layer is arranged between the first electrode and the
second electrode. The reflective layer is arranged on an opposite
side with respect to the luminescent layer with the first electrode
arranged between the reflective layer and the luminescent layer.
The reflective layer reflects light, which comes from the
luminescent layer, toward the second electrode. The transflective
layer is arranged in the same layer with the second electrode or
arranged on an opposite side with respect to the luminescent layer
with the second electrode arranged between the transflective layer
and the luminescent layer. Where .lamda. denotes a peak wavelength
of light that is emitted through the second electrode, .theta.1
denotes a phase shift (rad) of light having a wavelength .lamda.
when the light is reflected on the reflective layer, .theta.2 is a
phase shift (rad) of light having a wavelength .lamda. when the
light is reflected on the transflective layer, N is an integer that
is equal to or larger than 1, and N0 is an integer that is equal to
or larger than 1, an optical length L' between the reflective layer
and the transflective layer falls within a range that is expressed
by
0.8.times.(2.pi.N+.theta.1+.theta.2).times..lamda./(4.pi.).ltoreq.L'.ltor-
eq.1.2.times.(2.pi.N+.theta.1+.theta.2).times..lamda./(4.pi.), and
an optical length L'0 between a position, at which light is most
intensively generated in the luminescent layer, and the reflective
layer falls within a range that is expressed by
0.8.times.(2.pi.N0+.theta.1).times..lamda./(4.pi.).ltoreq.L'0.ltoreq.1.2.-
times.(2.pi.N0+.theta.1).times..lamda./(4.pi.).
Inventors: |
ODA; Toshihiro;
(Fujimi-machi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
Seiko Epson Corporation
Tokyo
JP
|
Family ID: |
40345817 |
Appl. No.: |
12/185499 |
Filed: |
August 4, 2008 |
Current U.S.
Class: |
313/504 |
Current CPC
Class: |
H01L 51/5265 20130101;
H01L 51/0078 20130101; H01L 51/006 20130101 |
Class at
Publication: |
313/504 |
International
Class: |
H01L 51/54 20060101
H01L051/54 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 2007 |
JP |
2007-205041 |
Claims
1. An organic electroluminescent device comprising: substrate; a
transflective layer; a translucent first electrode between the
substrate and the transflective layer; a luminescent layer between
the first electrode and the transflective layer; and a reflective
layer that between the substrate and the luminescent layer, the
reflective layer reflecting light from the luminescent layer toward
the second electrode; and an optical length L' between the
reflective layer and the transflective layer falls within a range
that satisfies the following relationship:
0.8.times.(2.pi.N+.theta.1+.theta.2).times..lamda./(4.pi.).ltoreq.L'.ltor-
eq.1.2.times.(2.pi.N+.theta.1+.theta.2).times..lamda./(4.pi.), and
an optical length L'0 between the reflective layer and a position
at which light is most intensively generated in the luminescent
layer falls within a range that satisfies the following
relationship:
0.8.times.(2.pi.N0+.theta.1).times..lamda./(4.pi.).ltoreq.L'0.ltoreq.1.2.-
times.(2.pi.N0+.theta.1).times..lamda./(4.pi.) where: .lamda.
denotes a peak wavelength of light that is emitted through the
second electrode, .theta.1 denotes a phase shift (rad) of light
having a wavelength .lamda. when the light is reflected on the
reflective layer, .theta.2 is a phase shift (rad) of light having a
wavelength .lamda. when the light is reflected on the transflective
layer, N is an integer that is equal to or larger than 1, and N0 is
an integer that is equal to or larger than 1.
2. The organic electroluminescent according to claim 1, wherein the
transflective layer serves as a second electrode opposite from the
first electrode with the luminescent layer disposed
therebetween.
3. The organic electroluminescent according to claim 1, further
comprising a second electrode between the transflective layer and
the luminescent layer.
4. An organic electroluminescent device comprising: a light
emitting device of which the color of emitted light is red; a light
emitting device of which the color of emitted light is green; and a
light emitting device of which the color of emitted light is blue,
wherein each of the light emitting devices includes: a
transflective layer; a translucent first electrode between the
substrate and the transflective layer; a luminescent layer between
the first electrode and the transflective layer; and a reflective
layer that between the substrate and the luminescent layer, the
reflective layer reflecting light from the luminescent layer toward
the second electrode; and an optical length L' between the
reflective layer and the transflective layer falls within a range
that satisfies the following relationship:
0.8.times.(2.pi.N+.theta.1+.theta.2).times..lamda./(4.pi.).ltoreq.L'.ltor-
eq.1.2.times.(2.pi.N+.theta.1+.theta.2).times..lamda./(4.pi.), and
an optical length L'0 between the reflective layer and a position
at which light is most intensively generated in the luminescent
layer falls within a range that satisfies the following
relationship:
0.8.times.(2.pi.N0+.theta.1).times..lamda./(4.pi.).ltoreq.L'0.ltoreq.1.2.-
times.(2.pi.N0+.theta.1).times..lamda./(4.pi.) where: .lamda.
denotes a peak wavelength of light that is emitted through the
second electrode, .theta.1 denotes a phase shift (rad) of light
having a wavelength .lamda. when the light is reflected on the
reflective layer, .theta.2 is a phase shift (rad) of light having a
wavelength .lamda. when the light is reflected on the transflective
layer, N is an integer that is equal to or larger than 1, and N0 is
an integer that is equal to or larger than 1.
5. The organic electroluminescent according to claim 4, wherein the
transflective layer serves as a second electrode opposite from the
first electrode with the luminescent layer disposed
therebetween.
6. The organic electroluminescent according to claim 4, further
comprising a second electrode between the transflective layer and
the luminescent layer.
7. An organic electroluminescent device comprising: a light
emitting device of which the color of emitted light is red; a light
emitting device of which the color of emitted light is green; and a
light emitting device of which the color of emitted light is blue,
wherein each of the light emitting devices includes: substrate; a
transflective layer; a translucent first electrode between the
substrate and the transflective layer; a luminescent layer between
the first electrode and the transflective layer; and a reflective
layer that between the substrate and the luminescent layer, the
reflective layer reflecting light from the luminescent layer toward
the second electrode; and in each of the light emitting devices,
the luminescent layer includes a first luminescent layer of which
generated light has a peak intensity at a wavelength corresponding
to yellow color, orange color, or red color, and a second
luminescent layer of which generated light has a peak intensity at
a wavelength corresponding to cyan color or blue color, wherein the
first luminescent layer and the second luminescent layer are
laminated, in regard to the light emitting device of which the
color of emitted light is red, an optical length L'.sub.R between
the reflective layer and the transflective layer falls within a
range that is expressed by
0.8.times.(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub.-
R/(4.pi.).ltoreq.L'.sub.R.ltoreq.1.2.times.(2.pi.N.sub.R+.theta..sub.1R+.t-
heta..sub.2R).times..lamda..sub.R/(4.pi.), in regard to the light
emitting device of which the color of emitted light is red, an
optical length L'.sub.0R between a position, at which light is most
intensively generated in the first luminescent layer, and the
reflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.).ltor-
eq.L'.sub.0R.ltoreq.1.2.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda.-
.sub.R/(4.pi.), wherein where: .lamda..sub.R denotes a peak
wavelength of red light that is emitted through the second
electrode, .theta..sub.1R denotes a phase shift (rad) of light
having a wavelength .lamda..sub.R when the light is reflected on
the reflective layer, .theta..sub.2R denotes the phase shift (rad)
of light having a wavelength .lamda..sub.R when the light is
reflected on the transflective layer, N.sub.R denotes an integer
that is equal to or larger than 1, and N.sub.0R denotes an integer
that is equal to or larger than 1, and in regard to the light
emitting device of which the color of emitted light is red, an
optical length L'.sub.0R between a position, at which light is most
intensively generated in the first luminescent layer, and the
reflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.).ltor-
eq.L'.sub.0R.ltoreq.1.2.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda.-
.sub.R/(4.pi.), in regard to the light emitting device of which the
color of emitted light is green, an optical length L'.sub.0G
between a position, at which light is most intensively generated in
the first or second luminescent layer, and the reflective layer
falls within a range that is expressed by
0.8.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.).ltor-
eq.L'.sub.0G.ltoreq.1.2.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda.-
.sub.G/(4.pi.), wherein where: .lamda..sub.G denotes a peak
wavelength of green light that is emitted through the second
electrode, .theta..sub.1G denotes a phase shift (rad) of light
having a wavelength .lamda..sub.G when the light is reflected on
the reflective layer, .theta..sub.2G denotes the phase shift (rad)
of light having a wavelength .lamda..sub.G when the light is
reflected on the transflective layer, N.sub.G denotes an integer
that is equal to or larger than 1, and N.sub.0G denotes an integer
that is equal to or larger than 1, in regard to the light emitting
device of which the color of emitted light is blue, an optical
length L'.sub.B between the reflective layer and the transflective
layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub.-
B/(4.pi.).ltoreq.L'.sub.B.ltoreq.1.2.times.(2.pi.N.sub.B+.theta..sub.1B+.t-
heta..sub.2B).times..lamda..sub.B/(4.pi.), and in regard to the
light emitting device of which the color of emitted light is blue,
an optical length L'.sub.0B between a position, at which light is
most intensively generated in the second luminescent layer, and the
reflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.).ltor-
eq.L'.sub.0B.ltoreq.1.2.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda.-
.sub.B/(4.pi.), wherein where: .lamda..sub.B denotes a peak
wavelength of blue light that is emitted through the second
electrode, .theta..sub.1B denotes a phase shift (rad) of light
having a wavelength .lamda..sub.B when the light is reflected on
the reflective layer, .theta..sub.2B denotes the phase shift (rad)
of light having a wavelength .lamda..sub.B when the light is
reflected on the transflective layer, N.sub.B denotes an integer
that is equal to or larger than 1, and N.sub.0B denotes an integer
that is equal to or larger than 1.
8. The organic electroluminescent according to claim 7, wherein the
transflective layer serves as a second electrode opposite from the
first electrode with the luminescent layer disposed
therebetween.
9. The organic electroluminescent according to claim 7, further
comprising a second electrode between the transflective layer and
the luminescent layer.
10. An organic electroluminescent device comprising: a light
emitting device of which the color of emitted light is red; a light
emitting device of which the color of emitted light is green; and a
light emitting device of which the color of emitted light is blue,
wherein each of the light emitting devices includes: substrate; a
transflective layer; a translucent first electrode between the
substrate and the transflective layer; a luminescent layer between
the first electrode and the transflective layer; and a reflective
layer that between the substrate and the luminescent layer, the
reflective layer reflecting light from the luminescent layer toward
the second electrode; and in each of the light emitting devices,
the luminescent layer includes a red luminescent layer of which
generated light has a peak intensity at a wavelength corresponding
to red color, a green luminescent layer of which generated light
has a peak intensity at a wavelength corresponding to green color,
and a blue luminescent layer of which generated light has a peak
intensity at a wavelength corresponding to blue color, wherein the
red luminescent layer, the green luminescent layer, and the blue
luminescent layer are laminated, in regard to the light emitting
device of which the color of emitted light is red, an optical
length L'.sub.R between the reflective layer and the transflective
layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub.-
R/(4.pi.).ltoreq.L'.sub.R.ltoreq.1.2.times.(2.pi.N.sub.R+.theta..sub.1R+.t-
heta..sub.2R).times..lamda..sub.R/(4.pi.), and in regard to the
light emitting device of which the color of emitted light is red,
an optical length L'.sub.0R between a position, at which light is
most intensively generated in the red luminescent layer, and the
reflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.).ltor-
eq.L'.sub.0R.ltoreq.1.2.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda.-
.sub.R/(4.pi.), wherein where: .lamda..sub.R denotes a peak
wavelength of red light that is emitted through the second
electrode, .theta..sub.1R denotes a phase shift (rad) of light
having a wavelength .lamda..sub.R when the light is reflected on
the reflective layer, .theta..sub.2R denotes the phase shift (rad)
of light having a wavelength .lamda..sub.R when the light is
reflected on the transflective layer, N.sub.R denotes an integer
that is equal to or larger than 1, and N.sub.0R denotes an integer
that is equal to or larger than 1, in regard to the light emitting
device of which the color of emitted light is green, an optical
length L'.sub.G between the reflective layer and the transflective
layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub.-
G/(4.pi.).ltoreq.L'.sub.G.ltoreq.1.2.times.(2.pi.N.sub.G+.theta..sub.1G+.t-
heta..sub.2G).times..lamda..sub.G/(4.pi.), and in regard to the
light emitting device of which the color of emitted light is green,
an optical length L'.sub.0G between a position, at which light is
most intensively generated in the green luminescent layer, and the
reflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.).ltor-
eq.L'.sub.0G.ltoreq.1.2.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda.-
.sub.G/(4.pi.), wherein where: .lamda..sub.G denotes a peak
wavelength of green light that is emitted through the second
electrode, .theta..sub.1G denotes a phase shift (rad) of light
having a wavelength .lamda..sub.G when the light is reflected on
the reflective layer, .theta..sub.2G denotes the phase shift (rad)
of light having a wavelength .lamda..sub.G when the light is
reflected on the transflective layer, N.sub.G denotes an integer
that is equal to or larger than 1, and N.sub.0G denotes an integer
that is equal to or larger than 1, in regard to the light emitting
device of which the color of emitted light is blue, an optical
length L'.sub.B between the reflective layer and the transflective
layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub.-
B/(4.pi.).ltoreq.L'.sub.B.ltoreq.1.2.times.(2.pi.N.sub.B+.theta..sub.1B+.t-
heta..sub.2B).times..lamda..sub.B/(4.pi.), and in regard to the
light emitting device of which the color of emitted light is blue,
an optical length L'.sub.0B between a position, at which light is
most intensively generated in the blue luminescent layer, and the
reflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.).ltor-
eq.L'.sub.0B.ltoreq.1.2.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda.-
.sub.B/(4.pi.) wherein where: .lamda..sub.B denotes a peak
wavelength of blue light that is emitted through the second
electrode, .theta..sub.1B denotes a phase shift (rad) of light
having a wavelength .lamda..sub.B when the light is reflected on
the reflective layer, .theta..sub.2B denotes the phase shift (rad)
of light having a wavelength .lamda..sub.B when the light is
reflected on the transflective layer, N.sub.B denotes an integer
that is equal to or larger than 1, and N.sub.0B denotes an integer
that is equal to or larger than 1.
11. The organic electroluminescent according to claim 10, wherein
the transflective layer serves as a second electrode opposite from
the first electrode with the luminescent layer disposed
therebetween.
12. The organic electroluminescent according to claim 10, further
comprising a second electrode between the transflective layer and
the luminescent layer.
13. An electronic apparatus comprising the organic
electroluminescent device according to claim 1.
14. An electronic apparatus comprising the organic
electroluminescent device according to claim 4.
15. An electronic apparatus comprising the organic
electroluminescent device according to claim 7.
16. An electronic apparatus comprising the organic
electroluminescent device according to claim 10.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to an organic
electroluminescent device and an electronic apparatus.
[0003] 2. Related Art
[0004] An organic EL device (organic electroluminescent device),
that is, an OLED (organic light emitting diode) device, attracts
increasing attention as a light source that can achieve a thin and
light-weight display. A full-color display that uses organic EL
devices has a lot of advantages, such as (1) excellent color purity
and (2) small amount of power consumption.
[0005] In the field of organic EL device, it has been known that
light having a specific wavelength within light generated in a
luminescent layer is intensified through interference or resonance
and light having the other wavelength is attenuated, and then the
light is emitted. For example, Japanese Patent No. 2,797,883
describes that the peak wavelength of light that will be emitted is
adjusted in such a manner that a translucent reflective layer and a
reflective electrode are arranged on each side of a luminescent
layer, and the optical length between the translucent reflective
layer and the reflective electrode (between reflection planes) is
appropriately set. That is, the optical length between the
reflection planes is set in accordance with the peak wavelength of
light that will be emitted, so that the optical length may be set
so as to coincide with the phase of light having a specific
wavelength inside a resonant structure.
[0006] According to the above technology, for any pixels, output
colors of R (red), G (green) and B (blue) may be obtained even when
the luminescent color of each luminescent layer is the same, that
is, for example, white. In addition, when the luminescent color is
approximate to the color of light that will be emitted (for
example, when R light is emitted from a pixel that has a
luminescent layer that generates the light of R color, G light is
emitted from a pixel that has a luminescent layer that generates
the light of G color, and B light is emitted from a pixel that has
a luminescent layer that generates the light of B color), it is
possible to increase the color purity of light.
[0007] In the technology described in Japanese Patent No.
2,797,883, the optical length between the reflection planes is
intended to be optimized; however, the position of a luminescent
layer interposed between the reflection planes is not particularly
adjusted. That is, Japanese Patent No. 2,797,883 does not describe
an optical path from the luminescent layer to the reflective
electrode or an optical path from the luminescent layer to the
translucent reflective layer.
SUMMARY
[0008] An advantage of some aspects of the invention is that it
provides an organic electroluminescent device that is able to
increase the color purity of light to be emitted and increase the
ratio of emitted light to generated light, and it also provides an
electronic apparatus.
[0009] An aspect of the invention provides an organic
electroluminescent device. The organic electroluminescent device
includes a translucent first electrode, a translucent second
electrode, a luminescent layer, a reflective layer, and a
transflective layer. The luminescent layer is arranged between the
first electrode and the second electrode. The reflective layer is
arranged on an opposite side with respect to the luminescent layer
with the first electrode arranged between the reflective layer and
the luminescent layer. The reflective layer reflects light, which
comes from the luminescent layer, toward the second electrode. The
transflective layer is arranged in the same layer with the second
electrode or arranged on an opposite side with respect to the
luminescent layer with the second electrode arranged between the
transflective layer and the luminescent layer. Where .lamda.
denotes a peak wavelength of light that is emitted through the
second electrode, .theta..sub.1 denotes a phase shift (rad) of
light having a wavelength .lamda. when the light is reflected on
the reflective layer, .theta..sub.2 is a phase shift (rad) of light
having a wavelength .lamda. when the light is reflected on the
transflective layer, N is an integer that is equal to or larger
than 1, and N.sub.0 is an integer that is equal to or larger than
1, an optical length L' between the reflective layer and the
transflective layer falls within a range that is expressed by
0.8.times.(2.pi.N+.theta..sub.1+.theta..sub.2).times..lamda./(4.pi.).l-
toreq.L'.ltoreq.1.2.times.(2.pi.N+.theta..sub.1+.theta..sub.2).times..lamd-
a./(4.pi.) (In equation (1)), and an optical length L'.sub.0
between a position, at which light is most intensively generated in
the luminescent layer, and the reflective layer falls within a
range that is expressed by
0.8.times.(2.pi.N.sub.0+.theta..sub.1).times..lamda./(4.pi.).ltoreq.L'.su-
b.0.ltoreq.1.2.times.(2.pi.N.sub.0+.theta..sub.1).times..lamda./(4.pi.)
(In equation (2))
[0010] In this manner, because the optical length L' between the
reflective layer and the transflective layer falls within the range
that is expressed by In equation (1), it is possible to enhance the
color purity around the wavelength .lamda. within light that is
emitted through the second electrode, and, hence, it is possible to
increase the ratio of light having the wavelength .lamda. to the
light that is generated in the luminescent layer. Furthermore,
because the optical length L'0 between the position, at which light
is most intensively generated in the luminescent layer, and the
reflective layer falls within the range that is expressed by In
equation (2), it is possible to enhance the color purity around the
wavelength .lamda. within light that is emitted through the second
electrode, and, hence, it is possible to increase the ratio of
light having the wavelength .lamda. to the light that is generated
in the luminescent layer.
[0011] Another aspect of the invention provides an organic
electroluminescent device. The organic electroluminescent device
includes a light emitting device of which the color of emitted
light is red, a light emitting device of which the color of emitted
light is green, and a light emitting device of which the color of
emitted light is blue. Each of the light emitting devices includes
a translucent first electrode, a translucent second electrode, a
luminescent layer, a reflective layer, and a transflective layer.
The luminescent layer is arranged between the first electrode and
the second electrode. The reflective layer is arranged on an
opposite side with respect to the luminescent layer with the first
electrode arranged between the reflective layer and the luminescent
layer. The reflective layer reflects light, which comes from the
luminescent layer, toward the second electrode. The transflective
layer is arranged in the same layer with the second electrode or
arranged on an opposite side with respect to the luminescent layer
with the second electrode arranged between the transflective layer
and the luminescent layer. In each of the light emitting devices,
where .lamda. denotes a peak wavelength of light that is emitted
through the second electrode, .theta..sub.1 denotes a phase shift
(rad) of light having a wavelength .lamda. when the light is
reflected on the reflective layer, .theta..sub.2 is a phase shift
(rad) of light having a wavelength .lamda. when the light is
reflected on the transflective layer, N is an integer that is equal
to or larger than 1, and N.sub.0 is an integer that is equal to or
larger than 1, an optical length L' between the reflective layer
and the transflective layer falls within a range that is expressed
by
0.8.times.(2.pi.N+.theta..sub.1+.theta..sub.2).times..lamda./(4.pi.).l-
toreq.L'.ltoreq.1.2.times.(2.pi.N+.theta..sub.1+.theta..sub.2).times..lamd-
a./(4.pi.) (In equation (3)), and, in each of the light emitting
devices, an optical length L'.sub.0 between a position, at which
light is most intensively generated in the luminescent layer, and
the reflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.0+.theta..sub.1).times..lamda./(4.pi.).ltoreq.L'.su-
b.0.ltoreq.1.2.times.(2.pi.N.sub.0+.theta..sub.1).times..lamda./(4.pi.)
(In equation (4)).
[0012] In this manner, because, in each of the light emitting
devices, the optical length L' between the reflective layer and the
transflective layer falls within the range that is expressed by In
equation (3), it is possible to enhance the color purity around the
wavelength .lamda. within light that is emitted through the second
electrode, and, hence, it is possible to increase the ratio of
light having the wavelength .lamda. to the light that is generated
in the luminescent layer. Furthermore, because, in each of the
light emitting devices, the optical length L'.sub.0 between the
position, at which light is most intensively generated in the
luminescent layer, and the reflective layer falls within the range
that is expressed by In equation (4), it is possible to enhance the
color purity around the wavelength .lamda. within light that is
emitted through the second electrode, and, hence, it is possible to
increase the ratio of light having the wavelength .lamda. to the
light that is generated in the luminescent layer.
[0013] Further another aspect of the invention provides an organic
electroluminescent device. The organic electroluminescent device
includes a light emitting device of which the color of emitted
light is red, a light emitting device of which the color of emitted
light is green, and a light emitting device of which the color of
emitted light is blue. Each of the light emitting devices includes
a translucent first electrode, a translucent second electrode, a
luminescent layer, a reflective layer, and a transflective layer.
The luminescent layer is arranged between the first electrode and
the second electrode. The reflective layer is arranged on an
opposite side with respect to the luminescent layer with the first
electrode arranged between the reflective layer and the luminescent
layer. The reflective layer reflects light, which comes from the
luminescent layer, toward the second electrode. The transflective
layer is arranged in the same layer with the second electrode or
arranged on an opposite side with respect to the luminescent layer
with the second electrode arranged between the transflective layer
and the luminescent layer. In each of the light emitting devices,
the luminescent layer includes a first luminescent layer of which
generated light has a peak intensity at a wavelength corresponding
to yellow color, orange color, or red color, and a second
luminescent layer of which generated light has a peak intensity at
a wavelength corresponding to cyan color or blue color. The first
luminescent layer and the second luminescent layer are laminated.
In regard to the light emitting device of which the color of
emitted light is red, where .lamda..sub.R denotes a peak wavelength
of red light that is emitted through the second electrode,
.theta..sub.1R denotes a phase shift (rad) of light having a
wavelength .lamda..sub.R when the light is reflected on the
reflective layer, .theta..sub.2R denotes the phase shift (rad) of
light having a wavelength .lamda..sub.R when the light is reflected
on the transflective layer, N.sub.R denotes an integer that is
equal to or larger than 1, and N.sub.0R denotes an integer that is
equal to or larger than 1, an optical length L'.sub.R between the
reflective layer and the transflective layer falls within a range
that is expressed by
0.8.times.(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub.-
R/(4.pi.).ltoreq.L'.sub.R.ltoreq.1.2.times.(2.pi.N.sub.r+.theta..sub.1R+.t-
heta..sub.2R).times..lamda..sub.R/(4.lamda.) (In equation (5)),
and, in regard to the light emitting device of which the color of
emitted light is red, an optical length L'.sub.0R between a
position, at which light is most intensively generated in the first
luminescent layer, and the reflective layer falls within a range
that is expressed by
0.8.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.).ltor-
eq.L'.sub.0R.ltoreq.1.2.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda.-
.sub.R/(4.pi.) (In equation (6)), wherein, in regard to the light
emitting device of which the color of emitted light is green, where
.lamda..sub.G denotes a peak wavelength of green light that is
emitted through the second electrode, .theta..sub.1G denotes a
phase shift (rad) of light having a wavelength .lamda..sub.G when
the light is reflected on the reflective layer, .theta..sub.2G
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.G when the light is reflected on the transflective
layer, N.sub.G denotes an integer that is equal to or larger than
1, and N.sub.0G denotes an integer that is equal to or larger than
1, an optical length L'.sub.G between the reflective layer and the
transflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub.-
G/(4.pi.).ltoreq.L'.sub.G.ltoreq.1.2.times.(2.pi.N.sub.G+.theta..sub.1G+.t-
heta..sub.2G).times..lamda..sub.G/(4.pi.) (In equation (7)), and,
in regard to the light emitting device of which the color of
emitted light is green, an optical length L'.sub.0G between a
position, at which light is most intensively generated in the first
or second luminescent layer, and the reflective layer falls within
a range that is expressed by
0.8.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.).ltor-
eq.L'.sub.0G.ltoreq.1.2.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda.-
.sub.G/(4.pi.) (In equation (8)), wherein, in regard to the light
emitting device of which the color of emitted light is blue, where
.lamda..sub.B denotes a peak wavelength of blue light that is
emitted through the second electrode, .theta..sub.1B denotes a
phase shift (rad) of light having a wavelength .lamda..sub.B when
the light is reflected on the reflective layer, .theta..sub.2B
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.B when the light is reflected on the transflective
layer, N.sub.B denotes an integer that is equal to or larger than
1, and N.sub.0B denotes an integer that is equal to or larger than
1, an optical length L'.sub.B between the reflective layer and the
transflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub.-
B/(4.pi.).ltoreq.L'.sub.B.ltoreq.1.2.times.(2.pi.N.sub.B+.theta..sub.1B+.t-
heta..sub.2B).times..lamda..sub.B/(4.pi.) (In equation (9)), and,
in regard to the light emitting device of which the color of
emitted light is blue, an optical length L'.sub.0B between a
position, at which light is most intensively generated in the
second luminescent layer, and the reflective layer falls within a
range that is expressed by
0.8.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.).ltor-
eq.L'.sub.0B.ltoreq.1.2.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda.-
.sub.B/(4.pi.) (In equation (10)).
[0014] In this aspect as well, in each of the light emitting
devices, it is possible to enhance the color purity around the
wavelength .lamda. within light that is emitted through the second
electrode, and, hence, it is possible to increase the ratio of
light having the wavelength .lamda. to the light that is generated
in the luminescent layer.
[0015] Yet another aspect of the invention provides an organic
electroluminescent device. The organic electroluminescent device
includes a light emitting device of which the color of emitted
light is red, a light emitting device of which the color of emitted
light is green, and a light emitting device of which the color of
emitted light is blue. Each of the light emitting devices includes
a translucent first electrode, a translucent second electrode, a
luminescent layer, a reflective layer, and a transflective layer.
The luminescent layer is arranged between the first electrode and
the second electrode. The reflective layer is arranged on an
opposite side with respect to the luminescent layer with the first
electrode arranged between the reflective layer and the luminescent
layer. The reflective layer reflects light, which comes from the
luminescent layer, toward the second electrode. The transflective
layer is arranged in the same layer with the second electrode or
arranged on an opposite side with respect to the luminescent layer
with the second electrode arranged between the transflective layer
and the luminescent layer. In each of the light emitting devices,
the luminescent layer includes a red luminescent layer of which
generated light has a peak intensity at a wavelength corresponding
to red color, a green luminescent layer of which generated light
has a peak intensity at a wavelength corresponding to green color,
and a blue luminescent layer of which generated light has a peak
intensity at a wavelength corresponding to blue color. The red
luminescent layer, the green luminescent layer, and the blue
luminescent layer are laminated. In regard to the light emitting
device of which the color of emitted light is red, where
.lamda..sub.R denotes a peak wavelength of red light that is
emitted through the second electrode, .theta..sub.1R denotes a
phase shift (rad) of light having a wavelength .lamda..sub.R when
the light is reflected on the reflective layer, .theta..sub.2R
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.R when the light is reflected on the transflective
layer, N.sub.R denotes an integer that is equal to or larger than
1, and N.sub.0R denotes an integer that is equal to or larger than
1, an optical length L'.sub.R between the reflective layer and the
transflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub.-
R/(4.pi.).ltoreq.L'.sub.R<1.2.times.(2.pi.N.sub.R+.theta..sub.1R+.theta-
..sub.2R).times..lamda..sub.R/(4.pi.) (In equation (11)), and, in
regard to the light emitting device of which the color of emitted
light is red, an optical length L'.sub.0R between a position, at
which light is most intensively generated in the red luminescent
layer, and the reflective layer falls within a range that is
expressed by
0.8.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.).ltor-
eq.L'.sub.0R<1.2.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub-
.R/(4.pi.) (In equation (12)), wherein, in regard to the light
emitting device of which the color of emitted light is green, where
.lamda..sub.G denotes a peak wavelength of green light that is
emitted through the second electrode, .theta..sub.1G denotes a
phase shift (rad) of light having a wavelength .lamda..sub.G when
the light is reflected on the reflective layer, .theta..sub.2G
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.G when the light is reflected on the transflective
layer, N.sub.G denotes an integer that is equal to or larger than
1, and N.sub.0G denotes an integer that is equal to or larger than
1, an optical length L'.sub.G between the reflective layer and the
transflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub.-
G/(4.pi.).ltoreq.L'.sub.G.ltoreq.1.2.times.(2.pi.N.sub.G+.theta..sub.1G+.t-
heta..sub.2G).times..lamda..sub.G/(4.pi.) (In equation (13)), and,
in regard to the light emitting device of which the color of
emitted light is green, an optical length L'.sub.0G between a
position, at which light is most intensively generated in the green
luminescent layer, and the reflective layer falls within a range
that is expressed by
0.8.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.).ltor-
eq.L'.sub.0G.ltoreq.1.2.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda.-
.sub.G/(4.pi.) (In equation (14)), wherein, in regard to the light
emitting device of which the color of emitted light is blue, where
.lamda..sub.B denotes a peak wavelength of blue light that is
emitted through the second electrode, .theta..sub.1B denotes a
phase shift (rad) of light having a wavelength .lamda..sub.B when
the light is reflected on the reflective layer, .theta..sub.2B
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.B when the light is reflected on the transflective
layer, N.sub.B denotes an integer that is equal to or larger than
1, and N.sub.0B denotes an integer that is equal to or larger than
1, an optical length L'.sub.B between the reflective layer and the
transflective layer falls within a range that is expressed by
0.8.times.(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub.-
B/(4.pi.).ltoreq.L'.sub.B.ltoreq.1.2.times.(2.pi.N.sub.B+.theta..sub.1B+.t-
heta..sub.2B).times..lamda..sub.B/(4.pi.) (In equation (15)), and,
in regard to the light emitting device of which the color of
emitted light is blue, an optical length L'.sub.0B between a
position, at which light is most intensively generated in the blue
luminescent layer, and the reflective layer falls within a range
that is expressed by
0.8.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.).ltor-
eq.L'.sub.0B.ltoreq.1.2.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda.-
.sub.B/(4.pi.) (In equation (16)).
[0016] In this aspect as well, in each of the light emitting
devices, it is possible to enhance the color purity around the
wavelength .lamda. within light that is emitted through the second
electrode, and, hence, it is possible to increase the ratio of
light having the wavelength .lamda. to the light that is generated
in the luminescent layer.
[0017] Yet another aspect of the invention provides an electronic
apparatus. Because the electronic apparatus includes the above
described organic electroluminescent device, the electronic
apparatus is able to increase the color purity of light to be
emitted and increase the ratio of emitted light to generated light.
The above electronic apparatus, for example, includes various
devices provided with the organic electroluminescent device as an
image display device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0019] FIG. 1 is a cross-sectional view that schematically shows an
organic electroluminescent device according to a first embodiment
of the invention.
[0020] FIG. 2 is a graph that shows the internal emission spectrum
in a luminescent layer of the organic electroluminescent device
shown in FIG. 1.
[0021] FIG. 3 is a graph that shows the advantageous effect
according to the first embodiment.
[0022] FIG. 4 is another graph that shows the advantageous effect
according to the first embodiment.
[0023] FIG. 5 is further another graph that shows the advantageous
effect according to the first embodiment.
[0024] FIG. 6 is a cross-sectional view that schematically shows an
organic electroluminescent device according to a second embodiment
of the invention.
[0025] FIG. 7 is a cross-sectional view that schematically shows an
organic electroluminescent device according to a third embodiment
of the invention.
[0026] FIG. 8 is a perspective view that shows an electronic
apparatus that employs the organic electroluminescent device
according to the aspect of the invention.
[0027] FIG. 9 is a perspective view that shows another electronic
apparatus that employs the organic electroluminescent device
according to the aspect of the invention.
[0028] FIG. 10 is a perspective view that shows further another
electronic apparatus that employs the organic electroluminescent
device according to the aspect of the invention.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0029] Hereinafter, various embodiments according to the invention
will be described with reference to the accompanying drawings. Note
that, in the drawings, the ratio of dimension of each portion is
appropriately varied from the actual one.
First Embodiment
[0030] FIG. 1 is a cross-sectional view that schematically shows an
organic electroluminescent device 1 according to a first embodiment
of the invention. The organic electroluminescent (EL) device 1
includes a plurality of light emitting devices (pixels) 15 (15R,
15G, 15B) as shown in the drawing. The organic EL device 1
according to the present embodiment is used as a full-color image
display device. A light emitting device 15R is a light emitting
device of which the color of emitted light is red, a light emitting
device 15G is a light emitting device of which the color of emitted
light is green, and a light emitting device 15B is a light emitting
device of which the color of emitted light is blue. In the drawing,
only the three light emitting devices 15 are shown; however, a
larger number of the light emitting devices than that shown in the
drawing are actually provided. Hereinafter, the suffixes R, G, and
B of the components respectively correspond to the light emitting
devices 15R, 15G, and 15B.
[0031] The aspects of the invention may be applied not only to a
bottom emission type but also to a top emission type. The organic
EL device 1 shown in the drawing is a top emission type as an
example. The organic EL device 1 has a substrate 20. The substrate
20 may be, for example, formed of a transparent material, such as
glass, or may be, for example, formed of an opaque material, such
as ceramics and metal.
[0032] However, FIG. 1 schematically shows the embodiment, and,
although not shown in the drawing, TFTs (thin film transistors) and
wirings that supply power to the pixels and an inorganic insulator
layer that covers the TFTs and the wirings are arranged on the
substrate 20. In addition, although not shown in the drawing, a
known separation wall (separator) may be arranged.
[0033] The components of each light emitting device 15 on the
substrate 20 include a reflective layer 22, a transparent electrode
(first electrode) 24, a hole transport/injection layer 26, a
luminescent layer 28, an electron transport/injection layer 30, and
a transflective electrode (second electrode, transflective layer)
32. The reflective layer 22 is, for example, formed of a highly
reflective metal, such as aluminum and chromium. The reflective
layer 22 reflects light (which includes light from the luminescent
layer 28), which is transmitted through the transparent electrode
24 and advances thereto, upward in the drawing, that is, toward the
transflective electrode 32.
[0034] The transparent electrode 24 is, for example, formed of a
transparent material, such as ITO (indium tin oxide), ZnO (zinc
oxide) and IZO (indium zinc oxide). In the present embodiment, the
transparent electrode 24 is a pixel electrode provided in each of
the pixels (light emitting devices), and is, for example, an
anode.
[0035] The hole transport/injection layer 26 has, for example, a
double layer structure, and includes a hole injection layer
arranged adjacent to the transparent electrode 24 and a hole
transport layer arranged adjacent to the luminescent layer 28. The
hole injection layer may be, for example, formed of a hole
injection material, such as CuPc (copper phthalocyanine) or a
product named "HI-406" produced by Idemitsu Kosan Co., Ltd. The
hole transport layer may be, for example, formed of a hole
transport material, such as NPD
(N,N'-Bis(1-naphthyl)-N,N'diphenyl-4,4-biphenyl) or a product named
"HT-320" produced by Idemitsu Kosan Co., Ltd. However, the hole
transport/injection layer 26 may be a single layer that doubles the
functions of the hole transport layer and the hole injection
layer.
[0036] In the luminescent layer 28, positive holes derived from the
transparent electrode 24 and electrons derived from the
transflective electrode 32 are combined to thereby emit light. The
luminescent layer 28 in the present embodiment is a single layer.
Inside the luminescent layer 28, light is not generated with a
uniform intensity, but light is generated most intensively at a
certain plane (a plane perpendicular to the sheet of FIG. 1 and is
parallel to the boundary between the luminescent layer 28 and the
hole transport/injection layer 26 in the drawing) and light is
generated weakly at the other positions. In FIG. 1, a hypothetical
line 28RS indicates a plane at which light is most intensively
generated inside the luminescent layer 28R of the light emitting
device 15R, a hypothetical line 28GS indicates a plane at which
light is most intensively generated inside the luminescent layer
28G of the light emitting device 15G, and a hypothetical line 28BS
indicates a plane at which light is most intensively generated
inside the luminescent layer 28B of the light emitting device
15B.
[0037] The electron transport/injection layer 30 has, for example,
a double layer structure, and includes an electron transport layer
arranged adjacent to the luminescent layer 28 and an electron
injection layer arranged adjacent to the transflective electrode
32. The electron transport layer may be, for example, formed of an
electron transport material, such as Alq3 (Tris8-quinolinolato
aluminum complex). The electron injection layer may be, for
example, formed of an electron injection material, such as LiF
(lithium fluoride). However, the electron transport/injection layer
30 may be a single layer that doubles the functions of the electron
transport layer and the electron injection layer. The electron
transport/injection layer 30 may be provided with the same
thickness in the plurality of pixels (light emitting devices) (that
is, the electron transport/injection layers 30R, 30B, and 30G may
have the same thickness).
[0038] The transflective electrode 32 is, for example, formed of a
transflective metal material, such as MgAl, MgCu, MgAu and MgAg. In
the present embodiment, the transflective electrode 32 is a common
electrode that is provided commonly over the plurality of pixels
(light emitting devices) and is, for example, a cathode. The
transflective electrode 32 transmits a portion of light (which
includes light from the luminescent layer 28), which is transmitted
through the electron transport/injection layer 30 and advances
thereto, upward in the drawing and reflects the remaining portion
of light downward in the drawing, that is, toward the transparent
electrode 24.
[0039] Although not shown in the drawing, in order to protect
layers, such as the luminescent layer 28 of the organic EL device
1, against moisture and oxygen, the transflective electrode 32 may
be covered with a known sealing film or a known sealing cap may be
bonded to the substrate 20. In addition, when the organic EL device
1 is used as a color image display device, a color filter may be
arranged on the side from which light is emitted in order to
improve the color purity of emitted light. Note that providing a
sealing film or a sealing cap and arranging a color filter may be
not only employed in the present embodiment but also employed in
the following other embodiments.
[0040] In the above structure, in a light emitting device, as an
electric current flows between the transparent electrode 24 and the
transflective electrode 32, the luminescent layer 28 generates
light. Within light that is generated in the luminescent layer 28,
a portion of light that advances downward in the drawing is
reflected on the reflective layer 22 toward the transflective
electrode 32. In addition, a portion of light that advances from
the luminescent layer 28 upward in the drawing is transmitted
through the transflective electrode 32 and the remaining portion of
light is reflected toward the reflective layer 22. The above
described reflection is repeatedly performed. Thus, in each of the
light emitting devices 15, because of interference or resonance, a
portion of light having a specific wavelength is intensified and a
portion of light having the other wavelength is attenuated.
[0041] FIG. 2 is a graph that shows the internal emission spectrum
in the luminescent layer 28. That is, FIG. 2 shows the emission
spectrum of the luminescent layer 28 when interference or resonance
of light is not applied in the light emitting device 15. As shown
in FIG. 2, the luminescent layer 28, which is a single layer, emits
white light having three peaks at 620 nm (which corresponds to red
color), 540 nm (which corresponds to green color), and 470 nm
(which corresponds to blue color). Note that the luminescent layers
28R, 28G, and 28B do not need to emit the same white light, but
each of the luminescent layers may be configured to emit a selected
luminescent color. For example, the luminescent layer 28R may emit
red light that has a peak of emission spectrum at 620 nm, the
luminescent layer 28G may emit green light that has a peak of
emission spectrum at 540 nm, and the luminescent layer 28B may emit
blue light that has a peak of emission spectrum at 470 nm.
[0042] Through the above described interference or resonance, in
the light emitting device 15R, within white light that is generated
in the luminescent layer 28, red color is intensified and then
emitted from the transflective electrode 32. In the light emitting
device 15G, within white light that is generated in the luminescent
layer 28, green color is intensified and then emitted from the
transflective electrode 32. In the light emitting device 15B,
within white light that is generated in the luminescent layer 28,
blue color is intensified and then emitted from the transflective
electrode 32.
[0043] In order to emit light from the transflective electrode 32R
so that only red color is intensified in the light emitting device
15R, theoretically, In equation (17) and In equation (18) are
preferably satisfied, and, furthermore, Equation (19) and Equation
(20) are preferably satisfied. In equation (17) and In equation
(18) are derived from Equation (19) and Equation (20), which are
theoretical equalities, with a tolerance of .+-.20%. The reason why
the tolerance is given is that complex multiple reflection may
actually occur.
0.8.times.(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub-
.R/(4.pi.).ltoreq.L'.sub.R.ltoreq.1.2.times.(2.pi.N.sub.R+.theta..sub.1R+.-
theta..sub.2R).times..lamda..sub.R/(4.pi.) (17)
0.8.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.).lto-
req.L'.sub.0R.ltoreq.1.2.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda-
..sub.R/(4.pi.) (18)
(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub.R/(4.pi.)-
=L'.sub.R (19)
(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.)=L'.sub.0R
(20)
Here, .lamda..sub.R denotes the peak wavelength of red light
(.lamda..sub.R may be, for example, set to 620 nm) that is emitted
through the transflective electrode 32R, .theta..sub.1R denotes the
phase shift (rad) of light having a wavelength .lamda..sub.R when
the light is reflected on the reflective layer 22R, .theta..sub.2R
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.R when the light is reflected on the transflective
electrode 32R, N.sub.R denotes an integer that is equal to or
larger than 1, and N.sub.0R denotes an integer that is equal to or
larger than 1.
[0044] L'.sub.R in In equation (17) and Equation (19) denotes an
optical length in the light emitting device 15R between the
reflective layer 22R and the transflective electrode 32R, and is
expressed by Equation (21).
L R ' = iR = 1 X n iR d iR ( 21 ) ##EQU00001##
In Equation (21), n.sub.iR denotes the refractive index of a layer
in the light emitting device 15R, and d.sub.iR denotes the
thickness of a layer in the light emitting device 15R. In Equation
(21), iR ranges from 1 to X and denotes a layer between the
reflective layer 22R and the transflective electrode 32R. X is the
total number of these layers.
[0045] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.R in the light emitting device 15R between
the reflective layer 22R and the transflective electrode 32R is
expressed by Equation (22).
L'.sub.R=n.sub.1Rd.sub.1R+n.sub.2Rd.sub.2R+n.sub.3Rd.sub.3R+n.sub.4Rd.su-
b.4R (22)
Here, n.sub.1R denotes the refractive index of the transparent
electrode 24R, and d.sub.iR denotes the thickness of the
transparent electrode 24R. n.sub.2R denotes the refractive index of
the hole transport/injection layer 26R, and d.sub.2R denotes the
thickness of the hole transport/injection layer 26R. n.sub.3R
denotes the refractive index of the luminescent layer 28R, and
d.sub.3R denotes the thickness of the luminescent layer 28R.
n.sub.4R denotes the refractive index of the electron
transport/injection layer 30R, and d.sub.4R denotes the thickness
of the electron transport/injection layer 30R.
[0046] L'.sub.0R in In equation (18) and Equation (20) denotes the
optical length between the plane 28RS, at which light is most
intensively generated in the luminescent layer 28R, and the
reflective layer 22R, and is expressed by Equation (23).
L 0 R ' = n NR d N 1 R + iR = 1 M n iR d iR ( 23 ) ##EQU00002##
In Equation (23), n.sub.iR denotes the refractive index of a layer
in the light emitting device 15R, and d.sub.iR denotes the
thickness of a layer in the light emitting device 15R. In Equation
(23), iR ranges from 1 to M and denotes a layer between the
reflective layer 22R and the luminescent layer 28R. M is the total
number of these layers. n.sub.NR denotes the refractive index of
the luminescent layer 28R, dN.sub.1R denotes a distance between the
plane 28RS, at which light is most intensively generated in the
luminescent layer 28R, and the hole transport/injection layer
26R.
[0047] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.0R between the plane 28RS, at which light is
most intensively generated in the luminescent layer 28R, and the
reflective layer 22R is expressed by Equation (24).
L'.sub.0R=n.sub.3Rd.sub.31R+n.sub.1Rd.sub.1R+n.sub.2Rd.sub.2R
(24)
Here, d.sub.31R denotes a distance between the plane 28RS, at which
light is most intensively generated in the luminescent layer 28R,
and the hole transport/injection layer 26R.
[0048] For example, it is given that the transparent electrode 24R
is formed of ITO (of which the refractive index n.sub.1R is 1.899
with respect to light having a wavelength of 620 nm) with the
thickness d.sub.1R of 30 nm, the refractive index n.sub.2R of the
hole transport/injection layer 26R is 1.7 and the thickness
d.sub.2R of the hole transport/injection layer 26R is 215 nm, the
refractive index n.sub.3R of the luminescent layer 28R is 1.7 and
the thickness d.sub.3R of the luminescent layer 28R is 10 nm, and
the refractive index n.sub.4R of the electron transport/injection
layer 30R is 1.7 and the thickness d.sub.4R of the electron
transport/injection layer 30R is 65 nm. In this case, through
Equation (21) and eventually through Equation (22), the optical
length L'.sub.R in the light emitting device 15R between the
reflective layer 22R and the transflective electrode 32R is 549.97
nm.
[0049] In addition, it is given that the distance d.sub.31R between
the plane 28RS, at which light is most intensively generated in the
luminescent layer 28R, and the hole transport/injection layer 26R
is 5 nm. In this case, through Equation (23) and eventually through
Equation (24), the optical length L'.sub.0R in the light emitting
device 15R between the plane 28RS, at which light is most
intensively generated in the luminescent layer 28R, and the
reflective layer 22R is 430.97 nm.
[0050] In addition, it is given that the phase shift .theta..sub.1R
of light having a wavelength 620 nm, when the light is reflected on
the reflective layer 22R, is 2.527 (rad), the phase shift
.theta..sub.2R of light having a wavelength 620 nm, when the light
is reflected on the transflective electrode 32R, is 2.390 (rad),
N.sub.R is 1, and N.sub.0R is 1. In this case,
(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub.R/(4.pi.)=-
552.60 nm, so that the relationship of In equation (17) is
satisfied. In addition, in this case,
(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.)=434.68
nm, so that the relationship of In equation (18) is satisfied.
[0051] In order to emit light from the transflective electrode 32
in such a manner that only green color is intensified in the light
emitting device 15G, theoretically, In equation (25) and In
equation (26) are preferably satisfied, and, furthermore, Equation
(27) and Equation (28) are preferably satisfied. In equation (25)
and In equation (26) are derived from Equation (27) and Equation
(28), which are theoretical equalities, with a tolerance of
.+-.20%. The reason why the tolerance is given is that complex
multiple reflection may actually occur.
0.8.times.(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub-
.G/(4.pi.).ltoreq.L'.sub.G.ltoreq.1.2.times.(2.pi.N.sub.G+.theta..sub.1G+.-
theta..sub.2G).times..lamda..sub.G/(4.pi.) (25)
0.8.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.).lto-
req.L'.sub.0G.ltoreq.1.2.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda-
..sub.G/(4.pi.) (26)
(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub.G/(4.pi.)-
=L'.sub.G (27)
(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.)=L'.sub.0G
(28)
Here, .lamda..sub.G denotes the peak wavelength of green light
(.lamda..sub.G may be, for example, set to 540 nm) that is emitted
through the transflective electrode 32G, .theta..sub.1G denotes the
phase shift (rad) of light having a wavelength .lamda..sub.G when
the light is reflected on the reflective layer 22G, .theta..sub.2G
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.G when the light is reflected on the transflective
electrode 32G, N.sub.G denotes an integer that is equal to or
larger than 1, and N.sub.0G denotes an integer that is equal to or
larger than 1.
[0052] L'.sub.G in In equation (25) and Equation (27) denotes an
optical length in the light emitting device 15G between the
reflective layer 22G and the transflective electrode 32G, and is
expressed by Equation (29).
L G ' = iG = 1 X n iG d iG ( 29 ) ##EQU00003##
In Equation (29), n.sub.iG denotes the refractive index of a layer
in the light emitting device 15G, and d.sub.iG denotes the
thickness of a layer in the light emitting device 15G. In Equation
(29), iG ranges from 1 to X and denotes a layer between the
reflective layer 22G and the transflective electrode 32G. X is the
total number of these layers.
[0053] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.G in the light emitting device 15G between
the reflective layer 22G and the transflective electrode 32G is
expressed by Equation (30).
L'.sub.G=n.sub.1G+d.sub.1G+n.sub.2G+d.sub.2G+n.sub.3Gd.sub.3G+n.sub.4Gd.-
sub.4G (30)
Here, n.sub.1G denotes the refractive index of the transparent
electrode 24G, and d.sub.1G denotes the thickness of the
transparent electrode 24G. n.sub.2G denotes the refractive index of
the hole transport/injection layer 26G, and d.sub.2G denotes the
thickness of the hole transport/injection layer 26G. n.sub.3G
denotes the refractive index of the luminescent layer 28G, and
d.sub.3G denotes the thickness of the luminescent layer 28G.
n.sub.4G denotes the refractive index of the electron
transport/injection layer 30G, and d.sub.4G denotes the thickness
of the electron transport/injection layer 30G.
[0054] L'.sub.0G in In equation (26) and Equation (28) denotes the
optical length between the plane 28GS, at which light is most
intensively generated in the luminescent layer 28G, and the
reflective layer 22G, and is expressed by Equation (31).
L 0 G ' = n NG d N 1 G + iG = 1 M n iG d iG ( 31 ) ##EQU00004##
In Equation (31), n.sub.iG denotes the refractive index of a layer
in the light emitting device 15G, and d.sub.iG denotes the
thickness of a layer in the light emitting device 15G. In Equation
(31), iG ranges from 1 to M and denotes a layer between the
reflective layer 22G and the luminescent layer 28G. M is the total
number of these layers. n.sub.NG denotes the refractive index of
the luminescent layer 28G, d.sub.N1G denotes a distance between the
plane 28GS, at which light is most intensively generated in the
luminescent layer 28G, and the hole transport/injection layer
26G.
[0055] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.0G between the plane 28GS, at which light is
most intensively generated in the luminescent layer 28G, and the
reflective layer 22G is expressed by Equation (32).
L'.sub.0G=n.sub.3Gd.sub.31G+n.sub.1Gd.sub.1G+n.sub.2Gd.sub.2G
(32)
Here, d.sub.31G denotes a distance between the plane 28GS, at which
light is most intensively generated in the luminescent layer 28G,
and the hole transport/injection layer 26G.
[0056] For example, it is given that the transparent electrode 24G
is formed of ITO (of which the refractive index n.sub.1G is 1.972
with respect to light having a wavelength of 540 nm) with the
thickness d.sub.1G of 30 nm, the refractive index n.sub.2G of the
hole transport/injection layer 26G is 1.7 and the thickness
d.sub.2G of the hole transport/injection layer 26G is 178 nm, the
refractive index n.sub.3G of the luminescent layer 28G is 1.7 and
the thickness d.sub.3G of the luminescent layer 28G is 10 nm, and
the refractive index n.sub.4G of the electron transport/injection
layer 30G is 1.7 and the thickness d.sub.4G of the electron
transport/injection layer 30G is 53 nm. In this case, through
Equation (29) and eventually through Equation (30), the optical
length L'.sub.G in the light emitting device 15G between the
reflective layer 22G and the transflective electrode 32G is 468.86
nm.
[0057] In addition, it is given that the distance d.sub.31G between
the plane 28GS, at which light is most intensively generated in the
luminescent layer 28G, and the hole transport/injection layer 26G
is 5 nm. In this case, through Equation (31) and eventually through
Equation (32), the optical length L'.sub.0G in the light emitting
device 15G between the plane 28GS, at which light is most
intensively generated in the luminescent layer 28G, and the
reflective layer 22G is 370.26 nm.
[0058] In addition, it is given that the phase shift .theta..sub.1G
of light having a wavelength 540 nm, when the light is reflected on
the reflective layer 22G, is 2.445 (rad), the phase shift
.theta..sub.2G of light having a wavelength 540 nm, when the light
is reflected on the transflective electrode 32G, is 2.278 (rad),
N.sub.G is 1, and N.sub.0G is 1, In this case,
(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub.G/(4.pi.)=-
472.96 nm, so that the relationship of In equation (25) is
satisfied. In addition, in this case,
(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.)=375.067
nm, so that the relationship of In equation (26) is satisfied.
[0059] In order to emit light from the transflective electrode 32
in such a manner that only blue color is intensified in the light
emitting device 15B, theoretically, In equation (33) and In
equation (34) are preferably satisfied, and, furthermore, Equation
(35) and Equation (36) are preferably satisfied. In equation (33)
and In equation (34) are derived from Equation (35) and Equation
(36), which are theoretical equalities, with a tolerance of
.+-.20%. The reason why the tolerance is given is that complex
multiple reflection may actually occur.
0.8.times.(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub-
.B/(4.pi.).ltoreq.L'.sub.B.ltoreq.1.2.times.(2.pi.N.sub.B+.theta..sub.1B+.-
theta..sub.2B).times..lamda..sub.B/(4.pi.) (33)
0.8.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.).lto-
req.L'.sub.0B.ltoreq.1.2.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda-
..sub.B/(4.pi.) (34)
(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub.B/(4.pi.)-
=L'.sub.B (35)
(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.)=L'.sub.0B
(36)
Here, .lamda..sub.B denotes the peak wavelength of blue light
(.lamda..sub.B may be, for example, set to 470 nm) that is emitted
through the transflective electrode 32B, .theta..sub.1B denotes the
phase shift (rad) of light having a wavelength .lamda..sub.B when
the light is reflected on the reflective layer 22B, .theta..sub.2B
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.B when the light is reflected on the transflective
electrode 32B, N.sub.B denotes an integer that is equal to or
larger than 1, and N.sub.0B denotes an integer that is equal to or
larger than 1.
[0060] L'.sub.B in In equation (33) and Equation (35) denotes an
optical length in the light emitting device 15B between the
reflective layer 22B and the transflective electrode 32B, and is
expressed by Equation (37)
L B ' = iB = 1 x n iB d iB ( 37 ) ##EQU00005##
In Equation (37), n.sub.iB denotes the refractive index of a layer
in the light emitting device 15B, and d.sub.iB denotes the
thickness of a layer in the light emitting device 15. In Equation
(37), iB ranges from 1 to X and denotes a layer between the
reflective layer 22B and the transflective electrode 32B. X is the
total number of these layers.
[0061] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.B in the light emitting device 15B between
the reflective layer 22B and the transflective electrode 32B is
expressed by Equation (38).
L'.sub.B=n.sub.1Bd.sub.1B+n.sub.2Bd.sub.2B+n.sub.3Bd.sub.3B+n.sub.4Bd.su-
b.4B (38)
Here, n.sub.1B denotes the refractive index of the transparent
electrode 24B, and d.sub.1B denotes the thickness of the
transparent electrode 24B. n.sub.2B denotes the refractive index of
the hole transport/injection layer 26B, and d.sub.2B denotes the
thickness of the hole transport/injection layer 26B. n.sub.3B
denotes the refractive index of the luminescent layer 28B, and
d.sub.3B denotes the thickness of the luminescent layer 28B.
n.sub.4B denotes the refractive index of the electron
transport/injection layer 30B, and d.sub.4B denotes the thickness
of the electron transport/injection layer 30B.
[0062] L'.sub.0B in In equation (34) and Equation (36) denotes the
optical length between the plane 28BS, at which light is most
intensively generated in the luminescent layer 28B, and the
reflective layer 22B, and is expressed by Equation (39).
L 0 B ' = n NB d N 1 B + iB = 1 M n iB d iB ( 39 ) ##EQU00006##
In Equation (39), n.sub.iB denotes the refractive index of a layer
in the light emitting device 15B, and d.sub.iB denotes the
thickness of a layer in the light emitting device 15B. In Equation
(39), iB ranges from 1 to M and denotes a layer between the
reflective layer 22B and the luminescent layer 28B. M is the total
number of these layers. n.sub.NB denotes the refractive index of
the luminescent layer 28B, d.sub.N1B denotes a distance between the
plane 28BS, at which light is most intensively generated in the
luminescent layer 28B, and the hole transport/injection layer
26B.
[0063] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.0B between the plane 28BS, at which light is
most intensively generated in the luminescent layer 28B, and the
reflective layer 22B is expressed by Equation (40).
L'.sub.0B=n.sub.3Bd.sub.31B+n.sub.1Bd.sub.1B+n.sub.2Bd.sub.2B
(40)
Here, d.sub.31B denotes a distance between the plane 28BS, at which
light is most intensively generated in the luminescent layer 28B,
and the hole transport/injection layer 26B.
[0064] For example, it is given that the transparent electrode 24B
is formed of ITO (of which the refractive index n.sub.1B is 2.043
with respect to light having a wavelength of 470 nm) with the
thickness d.sub.1B of 30 nm, the refractive index n.sub.2B of the
hole transport/injection layer 26B is 1.7 and the thickness
d.sub.2B of the hole transport/injection layer 26B is 146 am, the
refractive index n.sub.3B of the luminescent layer 28B is 1.7 and
the thickness d.sub.3B of the luminescent layer 28B is 10 nm, and
the refractive index n.sub.4B of the electron transport/injection
layer 30B is 1.7 and the thickness d.sub.4B of the electron
transport/injection layer 30B is 42 nm. In this case, through
Equation (37) and eventually through Equation (38), the optical
length L'.sub.B in the light emitting device 15B between the
reflective layer 22B and the transflective electrode 32B is 397.89
nm.
[0065] In addition, it is given that the distance d.sub.31B between
the plane 28BS, at which light is most intensively generated in the
luminescent layer 28B, and the hole transport/injection layer 26B
is 5 nm. In this case, through Equation (39) and eventually through
Equation (40), the optical length L'.sub.0B in the light emitting
device 15B between the plane 28BS, at which light is most
intensively generated in the luminescent layer 28B, and the
reflective layer 22B is 317.99 nm.
[0066] In addition, it is given that the phase shift .theta..sub.1B
of light having a wavelength 470 nm, when the light is reflected on
the reflective layer 22B, is 2.343 (rad), the phase shift
.theta..sub.2B of light having a wavelength 470 nm, when the light
is reflected on the transflective electrode 32B, is 2.154 (rad),
N.sub.B is 1, and N.sub.0B is 1. In this case,
(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub.B/(4.pi.)=-
403.19 nm, so that the relationship of In equation (33) is
satisfied. In addition, in this case,
(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.)=322.63
nm, so that the relationship of In equation (34) is satisfied.
[0067] In summary, it is preferable that, in each of the light
emitting devices 15, the optical length L' between the reflective
layer 22 and the transflective electrode 32 falls within the range
expressed by In equation (41), and in each of the light emitting
devices 15, the optical length L'0 between the position, that is,
the plane, at which light is most intensively generated in the
luminescent layer 28, and the reflective layer 22 falls within the
range expressed by In equation (42).
0.8.times.(2.pi.N+.theta.1+.theta.2).times..lamda./(4.pi.).ltoreq.L'.lto-
req.1.2.times.(2.pi.N+.theta.1+.theta.2).times..lamda./(4.pi.)
(41)
0.8.times.(2.pi.N0+.theta.1).times..lamda./(4.pi.).ltoreq.L'0.ltoreq.1.2-
.times.(2.pi.N0+.theta.1).times..lamda./(4.pi.) (42)
[0068] Here, .lamda. denotes the peak wavelength of light that is
emitted through the transflective electrode 32, .theta.1 denotes
the phase shift (rad) of light having a wavelength .lamda. when the
light is reflected on the reflective layer 22, .theta.2 denotes the
phase shift (rad) of light having a wavelength .lamda. when the
light is reflected on the transflective electrode 32, N denotes an
integer that is equal to or larger than 1, and N0 denotes an
integer that is equal to or larger than 1.
[0069] In order to ascertain whether the derived optical lengths
L'.sub.0R, L'.sub.0G, and L'.sub.0B are optimal, simulation was
performed. In the simulation, the spectra were obtained in such a
manner that the optical lengths L'.sub.R, L'.sub.G, and L'.sub.B
were fixed and the optical lengths L'.sub.0R, L'.sub.0G, and
L'.sub.0B were varied.
[0070] FIG. 3 is a graph that shows the spectra that were obtained
in such a manner that, in the light emitting device 15R, the
optical length L'.sub.R was fixed to 549.97 nm (which is the result
obtained through Equation (22)) and the optical length L'.sub.0R
was varied. Specifically, the optical length L'.sub.0R was varied
by varying the thickness d.sub.2R of the hole transport/injection
layer 26R, and the optical length L'.sub.R was maintained at a
fixed value in such a manner that the variation in the thickness
d.sub.2R of the hole transport/injection layer 26R was cancelled by
a variation in the thickness d.sub.4R of the electron
transport/injection layer 30R.
[0071] As is apparent from FIG. 3, the spectrum, of which L'.sub.0R
is 439.47 nm, is the best, and this result satisfies the
relationship of In equation (18).
[0072] FIG. 4 is a graph that shows the spectra that were obtained
in such a manner that, in the light emitting device 15G, the
optical length L'.sub.G was fixed to 468.86 nm (which is the result
obtained through Equation (30)) and the optical length L'.sub.0G
was varied. Specifically, the optical length L'.sub.0G was varied
by varying the thickness d.sub.2G of the hole transport/injection
layer 26G, and the optical length L'.sub.G was maintained at a
fixed value in such a manner that the variation in the thickness
d.sub.2G of the hole transport/injection layer 26G was cancelled by
a variation in the thickness d.sub.4G of the electron
transport/injection layer 30G.
[0073] As is apparent from FIG. 4, the spectrum, of which L'.sub.0G
is 373.66 nm, is the best, and this result satisfies the
relationship of In equation (26).
[0074] FIG. 5 is a graph that shows the spectra that were obtained
in such a manner that, in the light emitting device 15B, the
optical length L'.sub.B was fixed to 397.89 nm (which is the result
obtained through Equation (38)) and the optical length L'.sub.0B
was varied. Specifically, the optical length L'.sub.0B was varied
by varying the thickness d.sub.2B of the hole transport/injection
layer 26B, and the optical length L'.sub.B was maintained at a
fixed value in such a manner that the variation in the thickness
d.sub.2B of the hole transport/injection layer 26B was cancelled by
a variation in the thickness d.sub.4B of the electron
transport/injection layer 30B.
[0075] As is apparent from FIG. 5, the spectrum, of which L'.sub.0B
is 324.79 nm, is the best, and this result satisfies the
relationship of In equation (34).
Second Embodiment
[0076] FIG. 6 is a cross-sectional view that schematically shows an
organic electroluminescent device 10 according to a second
embodiment of the invention. The same reference signs are used in
FIG. 6 to indicate the components that are common to those of the
first embodiment, and the description thereof will not be repeated
in detail. The organic EL device 10 according to the second
embodiment basically has the similar structure to that of the
organic EL device 1 according to the first embodiment. The
modification in regard to the first embodiment may also be applied
to the second embodiment.
[0077] However, the first embodiment has the single luminescent
layer 28, whereas the second embodiment shown in FIG. 6 has a pair
of laminated luminescent layers 38 and 39 that are arranged between
the hole transport/injection layer 26 and the electron
transport/injection layer 30. The luminescent layer 38 is a first
luminescent layer of which generated light has a peak intensity at
a wavelength corresponding to yellow color, orange color, or red
color. That is, as the first luminescent layer 38 is energized, the
first luminescent layer 38 generates light (which includes a light
component having a wavelength corresponding to red and green)
having a peak intensity at a wavelength corresponding to yellow
color, orange color or red color. On the other hand, the
luminescent layer 39 is a second luminescent layer of which
generated light has a peak intensity at a wavelength corresponding
to cyan color or blue color. That is, as the second luminescent
layer 39 is energized, the second luminescent layer 39 generates
light (which includes a light component having a wavelength
corresponding to blue and green) having a peak intensity at a
wavelength corresponding to cyan color or blue color. In FIG. 6,
the first luminescent layer 38 is arranged adjacent to the hole
transport/injection layer 26, and the second luminescent layer 39
is arranged adjacent to the electron transport/injection layer 30;
however, the order, that is, the positions of the luminescent
layers 38 and 39 may be interchanged.
[0078] Because the two color luminescent layers 38 and 39 are
laminated as described above, as the light emitting device 15 is
energized, the luminescent layers 38 and 39 of the light emitting
device 15 may cooperate to generate white light. However, in each
of the light emitting devices 15, because of interference or
resonance, a portion of light having a specific wavelength is
intensified and a portion of light having the other wavelength is
attenuated. That is, in the light emitting device 15R, within white
light that is generated in the luminescent layers 38 and 39
(particularly, light generated in the first luminescent layer 38),
red color is intensified and then emitted from the transflective
electrode 32. In the light emitting device 15G, within white light
that is generated in the luminescent layers 38 and 39, green color
is intensified and then emitted from the transflective electrode
32. In the light emitting device 15B, within white light that is
generated in the luminescent layers 38 and 39 (particularly, light
generated in the second luminescent layer 39), blue color is
intensified and then emitted from the transflective electrode
32.
[0079] Inside each of the luminescent layers 38 and 39, light is
not generated with a uniform intensity, but light is generated most
intensively at a certain plane (a plane perpendicular to the sheet
of FIG. 6 and is parallel to the boundary between the luminescent
layer 38 and the hole transport/injection layer 26 in the drawing)
and light is generated weakly at the other positions. In FIG. 6, a
hypothetical line 38RS indicates a plane at which light is most
intensively generated inside the luminescent layer 38R of the light
emitting device 15R, a hypothetical line 38GS indicates a plane at
which light is most intensively generated inside the luminescent
layer 38G of the light emitting device 15G, and a hypothetical line
39BS indicates a plane at which light is most intensively generated
inside the luminescent layer 39B of the light emitting device
15B.
[0080] In order to emit light from the transflective electrode 32R
so that only red color is intensified in the light emitting device
15R, theoretically, In equation (43) and In equation (44) are
preferably satisfied, and, furthermore, Equation (45) and Equation
(46) are preferably satisfied. In equation (43) and In equation
(44) are derived from Equation (45) and Equation (46), which are
theoretical equalities, with a tolerance of .+-.20%. The reason why
the tolerance is given is that complex multiple reflection may
actually occur.
0.8.times.(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub-
.R/(4.pi.).ltoreq.L'.sub.R.ltoreq.1.2.times.(2.pi.N.sub.R+.theta..sub.1R+.-
theta..sub.2R).times..lamda..sub.R/(4.pi.) (43 )
0.8.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.).lto-
req.L'.sub.0R.ltoreq.1.2.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda-
..sub.R/(4.pi.) (44)
(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub.R/(4.pi.)-
=L'.sub.R (45)
(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.)=L'.sub.0R
(46)
Here, .lamda..sub.R denotes the peak wavelength of red light
(.lamda..sub.R may be, for example, set to 620 nm) that is emitted
through the transflective electrode 32R, .theta..sub.1R denotes the
phase shift (rad) of light having a wavelength .lamda..sub.R when
the light is reflected on the reflective layer 22R, .theta..sub.2R
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.R when the light is reflected on the transflective
electrode 32R, N.sub.R denotes an integer that is equal to or
larger than 1, and N.sub.0R denotes an integer that is equal to or
larger than 1.
[0081] L'.sub.R in In equation (43) and Equation (45) denotes an
optical length in the light emitting device 15R between the
reflective layer 22R and the transflective electrode 32R, and is
expressed by Equation (47).
L R ' = iR = 1 X n iR d iR ( 47 ) ##EQU00007##
In Equation (47), n.sub.iR denotes the refractive index of a layer
in the light emitting device 15R, and d.sub.iR denotes the
thickness of a layer in the light emitting device 15R. In Equation
(47), iR ranges from 1 to X and denotes a layer between the
reflective layer 22R and the transflective electrode 32R. X is the
total number of these layers.
[0082] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.R in the light emitting device 15R between
the reflective layer 22R and the transflective electrode 32R is
expressed by Equation (48).
L'.sub.R=n.sub.1Rd.sub.1R+n.sub.2Rd.sub.2R+n.sub.3Rd.sub.3R+n.sub.4Rd.su-
b.4R+n.sub.5Rd.sub.5R (48)
Here, n.sub.1R denotes the refractive index of the transparent
electrode 24R, and d.sub.1R denotes the thickness of the
transparent electrode 24R. n.sub.2R denotes the refractive index of
the hole transport/injection layer 26R, and d.sub.2R denotes the
thickness of the hole transport/injection layer 26R. n.sub.3R
denotes the refractive index of the first luminescent layer 38R,
and d.sub.3R denotes the thickness of the first luminescent layer
38R. n.sub.4R denotes the refractive index of the second
luminescent layer 39R, and d.sub.4R denotes the thickness of the
second luminescent layer 39R. n.sub.5R denotes the refractive index
of the electron transport/injection layer 30R, and d.sub.5R denotes
the thickness of the electron transport/injection layer 30R.
[0083] L'.sub.0R in In equation (44) and Equation (46) denotes the
optical length between the plane 38RS, at which light is most
intensively generated in the first luminescent layer 38R, and the
reflective layer 22R, and is expressed by Equation (49).
L 0 R ' = n NR d N 1 R + iR = 1 M n iR d iR ( 49 ) ##EQU00008##
In Equation (49), n.sub.iR denotes the refractive index of a layer
in the light emitting device 15R, and d.sub.iR denotes the
thickness of a layer in the light emitting device 15R. In Equation
(49), iR ranges from 1 to N and denotes a layer between the
reflective layer 22R and the first luminescent layer 38R. X is the
total number of these layers. n.sub.NR denotes the refractive index
of the first luminescent layer 38R, d.sub.N1R denotes a distance
between the plane 38RS, at which light is most intensively
generated in the first luminescent layer 38R, and the hole
transport/injection layer 26R.
[0084] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.0R between the plane 38RS, at which light is
most intensively generated in the first luminescent layer 38R, and
the reflective layer 22R is expressed by Equation (50).
L'.sub.0R=n.sub.3Rd.sub.31R+n.sub.1Rd.sub.1R+n.sub.2Rd.sub.2R
(50)
Here, d.sub.31R denotes a distance between the plane 38RS, at which
light is most intensively generated in the first luminescent layer
38R, and the hole transport/injection layer 26R.
[0085] In order to emit light from the transflective electrode 32
in such a manner that only green color is intensified in the light
emitting device 15G, theoretically, In equation (51) and In
equation (52) are preferably satisfied, and, furthermore, Equation
(53) and Equation (54) are preferably satisfied. In equation (51)
and In equation (52) are derived from Equation (53) and Equation
(54), which are theoretical equalities, with a tolerance of
.+-.20%. The reason why the tolerance is given is that complex
multiple reflection may actually occur.
0.8.times.(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub-
.G/(4.pi.).ltoreq.L'.sub.G.ltoreq.1.2.times.(2.pi.N.sub.G+.theta..sub.1G+.-
theta..sub.2G).times..lamda..sub.G/(4.pi.) (51)
0.8.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.).lto-
req.L'.sub.0G.ltoreq.1.2.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda-
..sub.G/(4.pi.) (52)
(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub.G/(4.pi.)-
=L'.sub.G (53)
(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.)=L'.sub.0G
(54)
Here, .lamda..sub.G denotes the peak wavelength of green light
(.lamda..sub.G may be, for example, set to 540 nm) that is emitted
through the transflective electrode 32G, .theta..sub.1G denotes the
phase shift (rad) of light having a wavelength .lamda..sub.G when
the light is reflected on the reflective layer 22G, .theta..sub.2G
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.G when the light is reflected on the transflective
electrode 32G, N.sub.G denotes an integer that is equal to or
larger than 1, and N.sub.0G denotes an integer that is equal to or
larger than 1.
[0086] L'.sub.G in In equation (51) and Equation (53) denotes an
optical length in the light emitting device 15G between the
reflective layer 22G and the transflective electrode 32G, and is
expressed by Equation (55).
L G ' = iG = 1 X n iG d iG ( 55 ) ##EQU00009##
In Equation (55), n.sub.iG denotes the refractive index of a layer
in the light emitting device 15G, and d.sub.iG denotes the
thickness of a layer in the light emitting device 15G. In Equation
(55), iG ranges from 1 to X and denotes a layer between the
reflective layer 22G and the transflective electrode 32G. X is the
total number of these layers.
[0087] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.G in the light emitting device 15G between
the reflective layer 22G and the transflective electrode 32G is
expressed by Equation (56).
L'.sub.G=n.sub.1Gd.sub.1G+n.sub.2Gd.sub.2G+n.sub.3Gd.sub.3G+n.sub.4Gd.su-
b.4G+n.sub.5Gd.sub.5G (56)
Here, n.sub.1G denotes the refractive index of the transparent
electrode 24G, and d.sub.1G denotes the thickness of the
transparent electrode 24G. n.sub.2G denotes the refractive index of
the hole transport/injection layer 26G, and d.sub.2G denotes the
thickness of the hole transport/injection layer 26G. n.sub.3G
denotes the refractive index of the first luminescent layer 38G,
and d.sub.3G denotes the thickness of the first luminescent layer
38G. n.sub.4G denotes the refractive index of the second
luminescent layer 39G, and d.sub.4G denotes the thickness of the
second luminescent layer 39G. n.sub.5G denotes the refractive index
of the electron transport/injection layer 30G, and d.sub.5G denotes
the thickness of the electron transport/injection layer 30G.
[0088] L'.sub.0G in In equation (52) and Equation (54) denotes the
optical length between the plane 38GS, at which light is most
intensively generated in the first luminescent layer 38G, and the
reflective layer 22G, and is expressed by Equation (57).
L 0 G ' = n NG d N 1 G + iG = 1 M n iG d iG ( 57 ) ##EQU00010##
In Equation (57), n.sub.iG denotes the refractive index of a layer
in the light emitting device 15G, and d.sub.iG denotes the
thickness of a layer in the light emitting device 15G. In Equation
(57), iG ranges from 1 to M and denotes a layer between the
reflective layer 22G and the first luminescent layer 38G. N is the
total number of these layers. n.sub.NG denotes the refractive index
of the first luminescent layer 38G, d.sub.N1G denotes a distance
between the plane 38GS, at which light is most intensively
generated in the first luminescent layer 38G, and the hole
transport/injection layer 26G.
[0089] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.0G between the plane 38GS, at which light is
most intensively generated in the first luminescent layer 38G, and
the reflective layer 22G is expressed by Equation (58).
L'.sub.0G=n.sub.3Gd.sub.31G+n.sub.1Gd.sub.1G+n.sub.2Gd.sub.2G
(58)
Here, d.sub.31G denotes a distance between the plane 38GS, at which
light is most intensively generated in the first luminescent layer
38G, and the hole transport/injection layer 26G.
[0090] In order to emit light from the transflective electrode 32
in such a manner that only blue color is intensified in the light
emitting device 15B, theoretically, In equation (59) and In
equation (60) are preferably satisfied, and, furthermore, Equation
(61) and Equation (62) are preferably satisfied. In equation (59)
and In equation (60) are derived from Equation (61) and Equation
(62), which are theoretical equalities, with a tolerance of
.+-.20%. The reason why the tolerance is given is that complex
multiple reflection may actually occur.
0.8.times.(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub-
.B/(4.pi.).ltoreq.L'.sub.B.ltoreq.1.2.times.(2.pi.N.sub.B+.theta..sub.1B+.-
theta..sub.2B).times..lamda..sub.B/(4.pi.) (59)
0.8.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.).lto-
req.L'.sub.0B.ltoreq.1.2.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda-
..sub.B/(4.pi.) (60)
(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub.B/(4.pi.)-
=L'.sub.B (61)
(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.)=L'.sub.0B
(62)
Here, .lamda..sub.B denotes the peak wavelength of blue light
(.lamda..sub.B may be, for example, set to 470 nm) that is emitted
through the transflective electrode 32B, .theta..sub.1B denotes the
phase shift (rad) of light having a wavelength .lamda..sub.B when
the light is reflected on the reflective layer 22B, .theta..sub.2B
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.B when the light is reflected on the transflective
electrode 32B, N.sub.B denotes an integer that is equal to or
larger than 1, and N.sub.0B denotes an integer that is equal to or
larger than 1.
[0091] L'.sub.B in In equation (59) and Equation (61) denotes an
optical length in the light emitting device 15B between the
reflective layer 22B and the transflective electrode 32B, and is
expressed by Equation (63).
L B ' = iB = 1 X n iB d iB ( 63 ) ##EQU00011##
In Equation (63), n.sub.iB denotes the refractive index of a layer
in the light emitting device 15B, and d.sub.iB denotes the
thickness of a layer in the light emitting device 15B. In Equation
(63), iB ranges from 1 to X and denotes a layer between the
reflective layer 22B and the transflective electrode 32B. X is the
total number of these layers.
[0092] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.B in the light emitting device 15B between
the reflective layer 22B and the transflective electrode 32B is
expressed by Equation (64).
L'.sub.B=n.sub.1Bd.sub.1B+n.sub.2Bd.sub.2B+n.sub.3Bd.sub.3B+n.sub.4Bd.su-
b.4B+n.sub.5Bd.sub.5B (64)
Here, n.sub.1B denotes the refractive index of the transparent
electrode 24B, and d.sub.1B denotes the thickness of the
transparent electrode 24B. n.sub.2B denotes the refractive index of
the hole transport/injection layer 26B, and d.sub.2B denotes the
thickness of the hole transport/injection layer 26B. n.sub.3B
denotes the refractive index of the first luminescent layer 38B,
and d.sub.3B denotes the thickness of the first luminescent layer
38B. n.sub.4B denotes the refractive index of the second
luminescent layer 39B, and d.sub.4B denotes the thickness of the
second luminescent layer 39B. n.sub.5B denotes the refractive index
of the electron transport/injection layer 30B, and d.sub.5B denotes
the thickness of the electron transport/injection layer 30B.
[0093] L'.sub.0B in In equation (60) and Equation (62) denotes the
optical length between the plane 39BS, at which light is most
intensively generated in the second luminescent layer 39B, and the
reflective layer 22B, and is expressed by Equation (65).
L 0 B ' = n NB d N 1 B + iB = 1 M n iB d iB ( 65 ) ##EQU00012##
In Equation (65), n.sub.iB denotes the refractive index of a layer
in the light emitting device 15B, and d.sub.iB denotes the
thickness of a layer in the light emitting device 15B. In Equation
(65), iB ranges from 1 to M and denotes a layer between the
reflective layer 22B and the second luminescent layer 39B. M is the
total number of these layers. n.sub.NB denotes the refractive index
of the second luminescent layer 38B, d.sub.N1B denotes a distance
between the plane 39BS, at which light is most intensively
generated in the second luminescent layer 39B, and the first
luminescent layer 38B.
[0094] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.0B between the plane 39BS, at which light is
most intensively generated in the second luminescent layer 39B, and
the reflective layer 22B is expressed by Equation (66).
L'.sub.0B=n.sub.4Bd.sub.41B+n.sub.1Bd.sub.1B+n.sub.2Bd.sub.2B+n.sub.3Bd.-
sub.3B (66)
Here, d.sub.41B denotes a distance between the plane 39BS, at which
light is most intensively generated in the second luminescent layer
39B, and the first luminescent layer 38B.
[0095] In the second embodiment, the optical length L'.sub.0G in
the light emitting device 15G of which the color of emitted light
is green is an optical length between the plane 38GS, at which
light is most intensively generated in the first luminescent layer
38G, and the reflective layer 22G. However, the optical length
L'.sub.0G may be an optical length between the plane, at which
light is most intensively generated in the second luminescent layer
39G, and the reflective layer 22G. For example, when the intensity
of a component having a wavelength corresponding to green color
within light generated in the first luminescent layer 38G is higher
than that of a component having a wavelength corresponding to green
color within light generated in the second luminescent layer 39G,
the optical length L'.sub.0G is preferably an optical length
between the plane 38GS, at which light is most intensively
generated in the first luminescent layer 38G, and the reflective
layer 22G. In the reverse case, the optical length L'.sub.0G is
preferably an optical length between the planer at which light is
most intensively generated in the second luminescent layer 39G, and
the reflective layer 22G.
Third Embodiment
[0096] FIG. 7 is a cross-sectional view that schematically shows an
organic electroluminescent device 11 according to a third
embodiment of the invention. The same reference signs are used in
FIG. 7 to indicate the components that are common to those of the
first embodiment, and the description thereof will not be repeated
in detail. The organic EL device 11 according to the third
embodiment basically has the similar structure to that of the
organic EL device 1 according to the first embodiment. The
modification in regard to the first embodiment may also be applied
to the third embodiment.
[0097] The third embodiment shown in FIG. 7 has triple laminated
luminescent layers 47, 43, and 49 that are arranged between the
hole transport/injection layer 26 and the electron
transport/injection layer 30. The luminescent layer 47 is a red
luminescent layer of which generated light has a peak intensity at
a wavelength corresponding to red color. That is, as the red
luminescent layer 47 is energized, the red luminescent layer 47
generates light having a peak intensity at a wavelength
corresponding to red color. The luminescent layer 48 is a green
luminescent layer of which generated light has a peak intensity at
a wavelength corresponding to green color. That is, as the green
luminescent layer 48 is energized, the green luminescent layer 48
generates light having a peak intensity at a wavelength
corresponding to green color. The luminescent layer 49 is a blue
luminescent layer of which generated light has a peak intensity at
a wavelength corresponding to blue color. That is, as the blue
luminescent layer 49 is energized, the blue luminescent layer 49
generates light having a peak intensity at a wavelength
corresponding to blue color. In FIG. 7, the red luminescent layer
47 is arranged adjacent to the hole transport/injection layer 26,
and the blue luminescent layer 49 is arranged adjacent to the
electron transport/injection layer 30; however, the order, that is,
the positions of the luminescent layers 47, 48, and 49 are not
limited to the example shown in the drawing.
[0098] Because three color luminescent layers 47, 48, and 49 are
laminated as described above, as the light emitting device 15 is
energized, the luminescent layers 47, 48, and 49 of the light
emitting device 15 may cooperate to generate white light. However,
in each of the light emitting devices 15, because of interference
or resonance, a portion of light having a specific wavelength is
intensified and a portion of light having the other wavelength is
attenuated. That is, in the light emitting device 15R, within white
light that is generated in the luminescent layers 47, 48, and 49
(particularly, light generated in the red luminescent layer 47),
red color is intensified and then emitted from the transflective
electrode 32. In the light emitting device 15G, within white light
that is generated in the luminescent layers 47, 48, and 49
(particularly, light generated in the green luminescent layer 48),
green color is intensified and then emitted from the transflective
electrode 32. In the light emitting device 15B, within white light
that is generated in the luminescent layers 47, 48, and 49
(particularly, light generated in the blue luminescent layer 49),
blue color is intensified and then emitted from the transflective
electrode 32.
[0099] Inside each of the luminescent layers 47, 48, and 49, light
is not generated with a uniform intensity, but light is generated
most intensively at a certain plane (a plane perpendicular to the
sheet of FIG. 7 and is parallel to the boundary between the
luminescent layer 47 and the hole transport/injection layer 26 in
the drawing) and light is generated weakly at the other positions.
In FIG. 7, a hypothetical line 47RS indicates a plane at which
light is most intensively generated inside the red luminescent
layer 47R of the light emitting device 15R, a hypothetical line
48GS indicates a plane at which light is most intensively generated
inside the green luminescent layer 48G of the light emitting device
15G, and a hypothetical line 49BS indicates a plane at which light
is most intensively generated inside the blue luminescent layer 49B
of the light emitting device 15B.
[0100] In order to emit light from the transflective electrode 32R
so that only red color is intensified in the light emitting device
15R, theoretically, In equation (66) and In equation (67) are
preferably satisfied, and, furthermore, Equation (68) and Equation
(69) are preferably satisfied, In equation (66) and In equation
(67) are derived from Equation (68) and Equation (69), which are
theoretical equalities, with a tolerance of .+-.20%. The reason why
the tolerance is given is that complex multiple reflection may
actually occur.
0.8.times.(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub-
.R/(4.pi.).ltoreq.L'.sub.R.ltoreq.1.2.times.(2.pi.N.sub.R+.theta..sub.1R+.-
theta..sub.2R).times..lamda..sub.R/(4.pi.) (66)
0.8.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.).lto-
req.L'.sub.0R.ltoreq.1.2.times.(2.pi.N.sub.0R+.theta..sub.1R).times..lamda-
..sub.R/(4.pi.) (67)
(2.pi.N.sub.R+.theta..sub.1R+.theta..sub.2R).times..lamda..sub.R/(4.pi.)-
=L'.sub.R (68)
(2.pi.N.sub.0R+.theta..sub.1R).times..lamda..sub.R/(4.pi.)=L'.sub.0R
(69)
Here, .lamda..sub.R denotes the peak wavelength of red light
(.lamda..sub.R may be, for example, set to 620 nm) that is emitted
through the transflective electrode 32R, .theta..sub.1R denotes the
phase shift (rad) of light having a wavelength .lamda..sub.R when
the light is reflected on the reflective layer 22R, .theta..sub.2R
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.R when the light is reflected on the transflective
electrode 32R, N.sub.R denotes an integer that is equal to or
larger than 1, and NOR denotes an integer that is equal to or
larger than 1.
[0101] L'.sub.R in In equation (66) and Equation (68) denotes an
optical length in the light emitting device 15R between the
reflective layer 22R and the transflective electrode 32R, and is
expressed by Equation (70).
L R ' = iR = 1 X n iR d iR ( 70 ) ##EQU00013##
In Equation (70), n.sub.iR denotes the refractive index of a layer
in the light emitting device 15R, and d.sub.iR denotes the
thickness of a layer in the light emitting device 15R. In Equation
(70), iR ranges from 1 to X and denotes a layer between the
reflective layer 22R and the transflective electrode 32R. X is the
total number of these layers.
[0102] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.R in the light emitting device 15R between
the reflective layer 22R and the transflective electrode 32R is
expressed by Equation (71).
L'.sub.R=n.sub.1Rd.sub.1R+n.sub.2Rd.sub.2R+n.sub.3Rd.sub.3R+n.sub.4Rd.su-
b.4R+n.sub.5Rd.sub.5R+n.sub.6Rd.sub.6R (71)
Here, n.sub.1R denotes the refractive index of the transparent
electrode 24R, and d.sub.1R denotes the thickness of the
transparent electrode 24R. n.sub.2R denotes the refractive index of
the hole transport/injection layer 26R, and d.sub.2R denotes the
thickness of the hole transport/injection layer 26R. n.sub.3R
denotes the refractive index of the red luminescent layer 47R, and
d.sub.3R denotes the thickness of the red luminescent layer 47R.
n.sub.4R denotes the refractive index of the green luminescent
layer 48R, and d.sub.4R denotes the thickness of the green
luminescent layer 48R. n.sub.5R denotes the refractive index of the
blue luminescent layer 49R, and d.sub.5R denotes the thickness of
the blue luminescent layer 49R. n.sub.6R denotes the refractive
index of the electron transport/injection layer 30R, and d.sub.6R
denotes the thickness of the electron transport/injection layer
30R.
[0103] L'.sub.0R in In equation (67) and Equation (69) denotes the
optical length between the plane 47RS, at which light is most
intensively generated in the red luminescent layer 47R, and the
reflective layer 22R, and is expressed by Equation (72)
L 0 R ' = n NR d N 1 R + iR = 1 M n iR d iR ( 72 ) ##EQU00014##
In Equation (72), n.sub.iR denotes the refractive index of a layer
in the light emitting device 15R, and d.sub.iR denotes the
thickness of a layer in the light emitting device 15R. In Equation
(72), iR ranges from 1 to M and denotes a layer between the
reflective layer 22R and the red luminescent layer 47R. M is the
total number of these layers. n.sub.NR denotes the refractive index
of the red luminescent layer 47R, d.sub.N1R denotes a distance
between the plane 47RS, at which light is most intensively
generated in the red luminescent layer 47R, and the hole
transport/injection layer 26R.
[0104] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.0R between the plane 47RS, at which light is
most intensively generated in the red luminescent layer 47R, and
the reflective layer 22R is expressed by Equation (73).
L'.sub.0R=n.sub.3Rd.sub.31R+n.sub.1Rd.sub.1R+n.sub.2Rd.sub.2R
(73)
Here, d.sub.31R denotes a distance between the plane 47RS, at which
light is most intensively generated in the red luminescent layer
47R, and the hole transport/injection layer 26R.
[0105] In order to emit light from the transflective electrode 32
in such a manner that only green color is intensified in the light
emitting device 15G, theoretically, In equation (74) and In
equation (75) are preferably satisfied, and, furthermore, Equation
(76) and Equation (77) are preferably satisfied. In equation (74)
and In equation (75) are derived from Equation (76) and Equation
(77), which are theoretical equalities, with a tolerance of
.+-.20%. The reason why the tolerance is given is that complex
multiple reflection may actually occur.
0.8.times.(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub-
.G/(4.pi.).ltoreq.L'.sub.G.ltoreq.1.2.times.(2.pi.N.sub.G+.theta..sub.1G+.-
theta..sub.2G).times..lamda..sub.G/(4.pi.) (74)
0.8.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.).lto-
req.L'.sub.0G.ltoreq.1.2.times.(2.pi.N.sub.0G+.theta..sub.1G).times..lamda-
..sub.G/(4.pi.) (75)
(2.pi.N.sub.G+.theta..sub.1G+.theta..sub.2G).times..lamda..sub.G/(4.pi.)-
=L'.sub.G (76)
(2.pi.N.sub.0G+.theta..sub.1G).times..lamda..sub.G/(4.pi.)=L'.sub.0G
(77)
Here, .lamda..sub.G denotes the peak wavelength of green light
(.lamda..sub.G may be, for example, set to 540 nm) that is emitted
through the transflective electrode 32G, .theta..sub.1G denotes the
phase shift (rad) of light having a wavelength .lamda..sub.G when
the light is reflected on the reflective layer 22G, .theta..sub.2G
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.G when the light is reflected on the transflective
electrode 32G, N.sub.G denotes an integer that is equal to or
larger than 1, and N.sub.0G denotes an integer that is equal to or
larger than 1.
[0106] L'.sub.G in In equation (74) and Equation (76) denotes an
optical length in the light emitting device 15G between the
reflective layer 22G and the transflective electrode 32G, and is
expressed by Equation (78).
L G ' = iG = 1 X n iG d iG ( 78 ) ##EQU00015##
In Equation (78), n.sub.iG denotes the refractive index of a layer
in the light emitting device 15G, and d.sub.iG denotes the
thickness of a layer in the light emitting device 15G. In Equation
(78), iG ranges from 1 to X and denotes a layer between the
reflective layer 22G and the transflective electrode 32G. X is the
total number of these layers.
[0107] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.G in the light emitting device 15G between
the reflective layer 22G and the transflective electrode 32G is
expressed by Equation (79).
L'.sub.G=n.sub.1Gd.sub.1G+n.sub.2Gd.sub.2G+n.sub.3Gd.sub.3G+n.sub.4Gd.su-
b.4G+n.sub.5Gd.sub.5G+n.sub.6Gd.sub.6G (79)
Here, n.sub.1G denotes the refractive index of the transparent
electrode 24G, and d.sub.1G denotes the thickness of the
transparent electrode 24G. n.sub.2G denotes the refractive index of
the hole transport/injection layer 26G, and d.sub.2G denotes the
thickness of the hole transport/injection layer 26G. n.sub.3G
denotes the refractive index of the red luminescent layer 47G, and
d.sub.3G denotes the thickness of the red luminescent layer 47G.
n.sub.4G denotes the refractive index of the green luminescent
layer 48G, and d.sub.4G denotes the thickness of the green
luminescent layer 48G. n.sub.5G denotes the refractive index of the
blue luminescent layer 49G, and d.sub.5G denotes the thickness of
the blue luminescent layer 49G. n.sub.6G denotes the refractive
index of the electron transport/injection layer 30G, and d.sub.6G
denotes the thickness of the electron transport/injection layer
30G.
[0108] L'.sub.0G in In equation (75) and Equation (77) denotes the
optical length between the plane 48GS, at which light is most
intensively generated in the green luminescent layer 48G, and the
reflective layer 22G, and is expressed by Equation (80).
L 0 G ' = n NG d N 1 G + iG = 1 M n iG d iG ( 80 ) ##EQU00016##
In Equation (80), n.sub.iG denotes the refractive index of a layer
in the light emitting device 15G, and d.sub.iG denotes the
thickness of a layer in the light emitting device 15G. In Equation
(80), iG ranges from 1 to M and denotes a layer between the
reflective layer 22G and the green luminescent layer 48G. M is the
total number of these layers, n.sub.NG denotes the refractive index
of the green luminescent layer 48G, d.sub.N1G denotes a distance
between the plane 48GS, at which light is most intensively
generated in the green luminescent layer 48G, and the red
luminescent layer 47G.
[0109] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.0G between the plane 48GS, at which light is
most intensively generated in the green luminescent layer 48G, and
the reflective layer 22G is expressed by Equation (81),
L'.sub.0G=n.sub.4Gd.sub.41G+n.sub.1Gd.sub.1G+n.sub.2Gd.sub.2G+n.sub.3Gd.-
sub.3G (81)
Here, d.sub.41G denotes a distance between the plane 48GS, at which
light is most intensively generated in the green luminescent layer
48G, and the red luminescent layer 47G.
[0110] In order to emit light from the transflective electrode 32
in such a manner that only blue color is intensified in the light
emitting device 15B, theoretically, In equation (82) and In
equation (83) are preferably satisfied, and, furthermore, Equation
(84) and Equation (85) are preferably satisfied. In equation (82)
and In equation (83) are derived from Equation (84) and Equation
(85), which are theoretical equalities, with a tolerance of
.+-.20%. The reason why the tolerance is given is that complex
multiple reflection may actually occur.
0.8.times.(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub-
.B/(4.pi.).ltoreq.L'.sub.B.ltoreq.1.2.times.(2.pi.N.sub.B+.theta..sub.1B+.-
theta..sub.2B).times..lamda..sub.B/(4.pi.) (82)
0.8.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.).lto-
req.L'.sub.0B.ltoreq.1.2.times.(2.pi.N.sub.0B+.theta..sub.1B).times..lamda-
..sub.B/(4.pi.) (83)
(2.pi.N.sub.B+.theta..sub.1B+.theta..sub.2B).times..lamda..sub.B/(4.pi.)-
=L'.sub.B (84)
(2.pi.N.sub.0B+.theta..sub.1B).times..lamda..sub.B/(4.pi.)=L'.sub.0B
(85)
Here, .lamda..sub.B denotes the peak wavelength of blue light
(.lamda..sub.B may be, for example, set to 470 nm) that is emitted
through the transflective electrode 32B, .theta..sub.1B denotes the
phase shift (rad) of light having a wavelength .lamda..sub.B when
the light is reflected on the reflective layer 22B, .theta..sub.2B
denotes the phase shift (rad) of light having a wavelength
.lamda..sub.B when the light is reflected on the transflective
electrode 32B, N.sub.B denotes an integer that is equal to or
larger than 1, and N.sub.0B denotes an integer that is equal to or
larger than 1.
[0111] L'.sub.B in In equation (82) and Equation (84) denotes an
optical length in the light emitting device 15B between the
reflective layer 22B and the transflective electrode 32B, and is
expressed by Equation (86).
L B ' = iB = 1 X n iB d iB ( 86 ) ##EQU00017##
In Equation (86), n.sub.iB denotes the refractive index of a layer
in the light emitting device 15B, and d.sub.iB denotes the
thickness of a layer in the light emitting device 15B. In Equation
(86), iB ranges from 1 to X and denotes a layer between the
reflective layer 22B and the transflective electrode 32B. X is the
total number of these layers.
[0112] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.B in the light emitting device 15B between
the reflective layer 22B and the transflective electrode 32B is
expressed by Equation (87).
L'.sub.B=n.sub.1Bd.sub.1B+n.sub.2Bd.sub.2B+n.sub.3Bd.sub.3B+n.sub.4Bd.su-
b.4B+n.sub.5Bd.sub.5B+n.sub.6Bd.sub.6B (87)
Here, n.sub.1B denotes the refractive index of the transparent
electrode 24B, and d.sub.1B denotes the thickness of the
transparent electrode 24B. n.sub.2B denotes the refractive index of
the hole transport/injection layer 26B, and d.sub.2B denotes the
thickness of the hole transport/injection layer 26B. n.sub.3B
denotes the refractive index of the red luminescent layer 47B, and
d.sub.3B denotes the thickness of the red luminescent layer 47B.
n.sub.4B denotes the refractive index of the green luminescent
layer 48B and d.sub.4B denotes the thickness of the green
luminescent layer 48B. n.sub.5B denotes the refractive index of the
blue luminescent layer 49B, and d.sub.5B denotes the thickness of
the blue luminescent layer 49B. n.sub.6B denotes the refractive
index of the electron transport/injection layer 30B, and d.sub.6B
denotes the thickness of the electron transport/injection layer
30B.
[0113] L'.sub.0B in In equation (83) and Equation (85) denotes the
optical length between the plane 49BS, at which light is most
intensively generated in the blue luminescent layer 49B, and the
reflective layer 22B, and is expressed by Equation (88).
L 0 B ' = n NB d N 1 B + iB = 1 M n iB d iB ( 88 ) ##EQU00018##
In Equation (88), n.sub.iB denotes the refractive index of a layer
in the light emitting device 15B, and d.sub.iB denotes the
thickness of a layer in the light emitting device 15B. In Equation
(88), iB ranges from 1 to M and denotes a layer between the
reflective layer 22B and the blue luminescent layer 49B. M is the
total number of these layers. n.sub.NB denotes the refractive index
of the blue luminescent layer 49B, d.sub.N1B denotes a distance
between the plane 49BS, at which light is most intensively
generated in the blue luminescent layer 49B, and the green
luminescent layer 48B.
[0114] Specifically, in the embodiment shown in the drawing, the
optical length L'.sub.0B between the plane 49BS, at which light is
most intensively generated in the blue luminescent layer 49B, and
the reflective layer 22B is expressed by Equation (89).
L'.sub.0B=n.sub.5Bd.sub.51B+n.sub.1Bd.sub.1B+n.sub.2Bd.sub.2B+n.sub.3Bd.-
sub.3B+n.sub.4Bd.sub.4B (89)
Here, d.sub.51B denotes a distance between the plane 49BS, at which
light is most intensively generated in the blue luminescent layer
49B, and the green luminescent layer 48B.
Alternative Embodiments
[0115] In the organic EL devices 1, 10, and 11 according to the
above described embodiments, each of the luminescent layers is
formed of a low molecular material, and the layers from the anode
to the cathode are, for example, formed in a vacuum by means of a
deposition method, such as vapor deposition. However, each of the
luminescent layers may be formed of a macromolecular material, and
at least one of layers from the anode to the cathode may be formed
by means of a liquid supplying method, such as an ink jet method
and a dispenser method.
[0116] In addition, the layers from the anode to the cathode are
not limited to the layers shown in the drawings, but another layer
may also be provided.
[0117] In the organic EL devices 1, 10, and 11 according to the
above described embodiments, the reflective layer 22 is in contact
with the transparent electrode 24. However, for example, a layer
formed of an insulative transparent material, such as silicon
oxide, may be arranged between the reflective layer 22 and the
transparent electrode 24.
[0118] In the organic EL devices 1, 10, and 11 according to the
above described embodiments, the electrode and the transflective
layer are implemented as one transflective electrode 32. However,
the electrode 32 may be formed of a high translucent material, and
a transflective layer formed of a material that is different from
the material of the electrode 32 may be arranged on the opposite
side with respect to the luminescent layer 28 with the electrode 32
arranged between the transflective layer and the luminescent layer
28. Furthermore, a layer formed of a high translucent material may
be arranged between the electrode and the transflective layer.
[0119] The organic EL devices 1, 10, and 11 according to the above
described embodiments are of top emission type. However, the
aspects of the invention may be applied to a bottom emission type.
In the case of the bottom emission type, it is only necessary that
the reflective layer is arranged at a position farther from the
substrate than the transflective layer is, and the luminescent
layer is arranged between the reflective layer and the
transflective layer.
[0120] In the above described embodiments, the optical lengths
L'.sub.0R, L'.sub.0G, and L'.sub.0B are set in such a manner that
all the thicknesses d.sub.1R, d.sub.1G, and d.sub.1B of ITO are
made equal, and the thicknesses d.sub.2R, d.sub.2G, and d.sub.2B of
the hole transport/injection layers are respectively adjusted.
However, the optical lengths L'.sub.0R, L'.sub.0G, and L'.sub.0B
may also be set in such a manner that all the thicknesses d.sub.2R,
d.sub.2G, and d.sub.2B of the hole transport/injection layers are
made equal, and the thicknesses d.sub.1R, d.sub.1G, and d.sub.1B of
ITO are respectively adjusted. In this manner, it is possible to
form a plurality of pixels (light emitting devices) of the hole
transport/injection layers at the same time and, therefore, it is
advantageous in manufacturing.
Applications
[0121] Next, an electronic apparatus that employs the organic EL
device according to the aspects of the invention will be described.
FIG. 8 is a perspective view that shows the configuration of a
mobile personal computer that uses the organic EL device 1, 10 or
11 according to the above embodiments as an image display device.
The personal computer 2000 includes the organic EL device 1, which
serves as a display device, and a body portion 2010. The body
portion 2010 is provided with a power switch 2001 and a keyboard
2002. FIG. 9 is a view of a cellular phone that employs the organic
EL device 1, 10 or 11 according to the above embodiments. The
cellular phone 3000 includes a plurality of operating buttons 3001,
a plurality of scroll buttons 3002, and the organic EL device 1,
which serves as a display device. By manipulating the scroll
buttons 3002, an image displayed on the organic EL device 1 is
scrolled. FIG. 10 is a view of a personal digital assistant (PDA)
that employs the organic EL device 1, 10 or 11 according to the
above embodiments. The personal digital assistant 4000 includes a
plurality of operating buttons 4001, a power switch 4002, and the
organic EL device 1, which serves as a display device. As the power
switch 4002 is manipulated, various pieces of information, such as
an address book and a schedule book, are displayed on the organic
EL device 1.
[0122] The electronic apparatuses that employ the organic EL device
according to the aspects of the invention include, in addition to
the apparatuses shown in FIG. 8 to FIG. 10, a digital still camera,
a television, a video camera, a car navigation system, a pager, an
electronic personal organizer, an electronic paper, an electronic
calculator, a word processor, a workstation, a video telephone, a
POS terminal, a video player, and devices provided with a touch
panel.
* * * * *